Definitely a male! They do sniff, chase and mount each other to establish dominance - aslong as it doesn't turn nasty and they don't attack/bite each other they should be fine. It doesn't always work out but if Bolt is still very young he will probably just let Bud be in charge without putting up much of a fight because he's not at such a hormonal stage. I'd introduced my baby pig Godzilla to Nemo who is about 5 1/2 not so long ago and Godzilla is just so attached to Nemo now, it's like me and my shadow. They don't make any sort of displays at each other, just total calm, they get along great.
I'd carry on introducing Bolt and Bud in a neutral setting, such as the run, until you feel you are happy to put them in a cage/hutch together. I'd still have them somewhere you can watch them though just for a few days. Make sure any accomodation is throughly cleaned and disinfected before you do that, just to make sure it doesn't smell so much like Bud to prevent him becoming territorial. You can also put tea tree or something strong smelling like (just make sure it's got pig safe ingredients) that on their bums and noses so they basically smell the same to each other, that sometimes helps.