I think the OP wasn't saying that they're going to house their snake with another snake, but that since the ball was in with a boa at the store what possible health risks are there.
IBD is a fatal disease that can be spread from a boa to a python (and other boas), but honestly the threat of IBD is a a rare occurance though the fear of it is discussed all the time on different snake forums. I would say your BP is safe from IBD, I would just keep an eye on him for the usual health concerns such as RI, mites, regurging, etc: things that are caused by bad husbandry and not necissarily with being kept with a boa or another snake of a different species.
A pic would help with the BP's skin "issues" as well.