Should a Hadith from people of Bid'at/innovations be trusted/accepted?

Should a Hadith from someone in the chain of narration (Isnad) who practices a Bid'ah be accepted? I have heard that if it supports what he is practicing of Bid'ah then it is not accepted but if it does not support his practice it is OK. What if he didn't create that Bid'ah/innovation, and he is trustworthy and truthful, does the practicing of this Bid'ah affect the transmission of Hadith he has? What have scholars (looking for the views mainly of Bukari and or Muslim) said on this?