Answer: Yes, 99.9% of the time, Peanut Butter is vegan.
Summary: quality peanut butter is made from crushed peanuts and maybe a little bit of salt. Crappy peanut butter has hydrogenated oils and other goop added. But all those ingredients are from vegan friendly sources. Some peanut butters contain mono and diglycerides which can be from dubious sources (Jif Peanut Butter is one of those peanut butters). Other natural (and less natural) peanut butters contain honey as a natural sweetener. Best bet, watch out for crappy filler ingredients. Always buy peanut butter that is strictly peanuts. Even better, go to a store where you can grind the peanuts on demand. Nothing beats freshly ground peanut butter.