Halachically speaking, Can an Orthodox Jew attend a reform or Conservative burial?
I hunted a few web sites regarding what differences may be performed at a Reform burial. The only difference I could find is that Reform Jews allow the dead person to be buried in his clothes, whereas others have the dead buried in a tallit.
As for other practices, see this article. In here, the only differences seem to be related to the funeral and shiva customs. There does not seem to be any difference in the burial, itself, other than what I mentioned, above. Perhaps, the mourners, congregants say fewer prayers, say them in English, etc. However, IMO, these rituals should not prevent anyone from attending the burial. From what I gather, everything else, is the same. The body is buried; it's in a casket (I have heard that in Israel, particularly, there are some that don't bury the body in a casket, and that's a specific minhag.), etc.
If you are aware of any specific rituals that make a Reform burial different, please cite them. In any case, contact a rav (one that's alive, obviously :-) about what to do.