Hadiths do not originate from the person that tells you it - there is a solid chain narration that must be preserved when relating a hadith back to the Prophet SAW. In fact, if only the text of the hadith is presented to you without the chain of narration leading back to the Prophet SAW, then the hadith is considered incomplete.
If a person brings you the hadith with the proper chain of narration (the sanad), it is a fact - he is merely a messenger. Once he gives you the text of the hadith, the chain of narration, and the compilation in which it was found, then whatever this person said (no matter who he is, should he even be non-Muslim) can be readily proved or disproved, one way or the other.
In this day and age, most of the ahadith of the Prophet have been classified and vetted as being sahih (verified beyond the doubt, extremely accurate, and very reliable), hassan (verified and accurate), da'if (weak, doubt as to its authenticity), or mauwdoo' (known fabricated/false). This classification work was done by some of the greatest scholars of Islamic jurisprudence and history, and is preserved in their compendiums. This is what you should refer to when checking if a hadith is valid or otherwise.