The antipathy of the Judeans towards the Samaritans is well known. Is this simply because of the ethnicity ascribed to them in 2 Kings 17:24-26 and their unsanctioned temple, or were they also mortal enemies in the time of the Maccabees?
According to Jonathan Bourgel in his essay "The Samaritans during the Hasmonean Period: The Affirmation of a Discrete Identity?", there isn't any strong evidence for either option at the moment. On one hand, according to 2 Maccabees 6:1-2:
"Not long after that, the king sent an elderly Athenian to force the Jews to abandon their religion and the customs of their ancestors. He was also to defile their Temple by dedicating it to the Olympian god Zeus. The temple on Mount Gerizim was to be officially named Temple of Zeus the God of Hospitality, as the people who lived there had requested."
-like the Temple in Jerusalem, the temple in Mt. Gerizim was also defiled and repurposed, which would suggest the possibility of some form of kinship or an alliance between the Jews and the Samaritans against the Greeks.
But on the other hand:
"Here again, the category of Jews includes both the [Hashem] worshippers in Jerusalem and on Mt. Gerizim. However, the depiction of the Samaritans in this account remains a matter of controversy, much of this discussion depending on the meaning of the phrase [something in Greek]...none of the main explanations proposed is free of difficulties...many have inferred that the Mt. Gerizim temple was renamed after Zeus Xenios, at the request of the local inhabitants. this interpretation seemingly corresponds to the letter found in Josephus penned by the people referring to themselves as the "Sidonians in Shechem" and asking Antiochus IV to allow that their temple be renamed after Zeus Hellenios...There is, however, a noticeable discrepancy between the mention of Zeus Xenios...and that of Zeus Hellenios...As mentioned above...Josephus quotes a memorandum allegedly sent by the Samaritans to the Seleucid king...The authors of the missive, who described themselves as the "Sidonians in Shechem"...asked not to be persecuted as Jews on the grounds that they were of Sidonian sotck, and that although they observed the Sabbath and "offered the appropriate sacrifices", they practiced different customs from the Jews. In addition, they demanded that the temple on mount Gerizim be dedicated to Zeus Hellenios. Josephus, who identifies these Sidonians with the Samaritans, presents this letter as illustrating that the Samaritans were opportunists...Some scholars have assumed that they were reformed Hellenized Samaritans who sought to root themselves in Hellenistic culture...A further suggestion...that the Samaritans were called "Sidonians" simply because this name was tainted with the pejorative connotations in certain passages of Isaiah (23:2;4)..."
Meaning, there might have been a group of stray Samaritans who, like Hellenistic Jews, accepted the rule of the Greeks and worked against the Samaritans (and Jews).
Bourgel's mention of Josephus, however, is interesting, because it seems that even if one would argue that these "Sidonians" were a small sect and were not representative of the majority, the impression made on the Jews, especially as more and more years went by, was that the Samaritans as a whole were Grecian collaborators.
And later Bourgel writes:
"After the death of Judas (161 BCE), his brothers, Jonathan (161-142 BCE) and Simon (142-134 BCE), took the lead in the struggle against the Seleucids...Interestingly enough, the grant of these districts was supplemented by the award of exemption from all royal taxes for "all those who offer sacrifices in Jerusalem..." This clause, which certainly derived from a specific request of Jonathan (1 Macc 11:28), implies that those inhabitants of the three annexed districts who continued to bring sacrifices to the Samaritan temple on Mt. Gerizim were denied the exemptions. In other words, it seems that Jonathan used persuasion to convince those [Hashem] worshippers dwelling in the regions of Lydda, Aphairema and Ramathaim to recognize the Jerusalem temple as the only legitimate place of worship..."
To me, it seems that even if the Samaritans had attempted to side in the war with the Chashmonaim, they would have demanded to be allowed to keep their temple and to have it recognized as legitimate by the new rebel leadership, which would have probably resulted in having the demand denied, which would lead the Samaritans to probably having remained neutral (not having any particular love for the Greeks either).
So while they it seems unlikely that as a whole they were mortal enemies of the Jews, and most likely remained passive/inactive during the Chashmonaim-Grecian war, their style of worship was probably the main driving factor in growing tensions between the two groups. The problem doesn't seem to have been their ethnicity but their refusal to fall in line with the Judaic mainstream whilst continuing to pass themselves off as legitimate Jews (note that non-Jews can make sacrifices outside of the Temple in Jerusalem. If the Samaritans hadn't claimed they were Jews, and there wouldn't have been halachic debates on their status, I believe they would have been allowed to keep their temple as nothing more than a fancy altar).