yes, hes still fertile but a vet should be able to castrate him if you can feel the ball there.
if hes out with wethers it shouldnt be a problem. i have 2 billies together and they are fine. they dont bully eachother but they do playfight. my nannies are worst for bullying.
but he will be sexually mature at some point and start his mating rituals which can get very smelly.
was he sold as seen?