One subsite theme not compatible with Buddypress. Should use?

Not sure to post here in multisite or over in Buddypress.org but here it is anyway: I am building a multisite for e-commerce right now that has a community site with blog and bbpress and BP groups, an e-commerce store site, a marketplace site where users can resell things, and a sponsor directory site. The sponsor directory is a beautiful theme that does exactly what I need it to, only it isn’t Buddypress compatible. All the users will be browsing around all the subsites as if they were sections of the same site, so there isn’t a lot of separation other than different themes and css styling between the subsites. Wondering if there is going to be a problem going back and forth between the sponsor directory (non-BP compatible) site and the rest of the sites on the network. Anyone have any experience with this who can share thoughts or things to watch out for?