The Gemara in Chullin 95b says that if one relied on actions like Eliezer did, then that would violate Nichush. However, Rashi says that is only if one relies solely on the action without any reasoning behind it. See Tosfos there as well who explains that once Eliezer asked about her lineage, there was no longer a prohibition of Nichush [in my understandning, this means that once one looks for an explanation for an action, then it no longer falls under the prohibition of Nichush].
To use your examples, if one married a person based on a specific predicted action without examining the motivation, then yes, that would be Nichush. But determining based on reasons and character traits would not be Nichush.