I agree with you...most people (except BU fans) will be cheering against us. If DC was any example...and even in BOSTON in 2015 there were more people cheering for Providence.
Another BC fan here that will be strongly cheering you on in this year's Frozen 4. I too cheered on Providence that year and probably would cheer on any Hockey East school against BU in the NCAA's just as I suspect BU fans would do against BC. Playing Providence in Boston, BU was a formidable favorite and thus had a target on their back so other fans joined in against BU while in Tampa BU has to be considered the underdog although being the 5th seed really is not an underdog at all. Keep in mind that North Dakota brings as many fans as anyone and their dislike for Minnesota should be a big plus for BU too.