While I admit I personally don’t have much experience with current *BSDs (outside of running Darwin/OS X/iOS), I noticed this topic was sinking without an answer. That said, from what I’ve seen from building snapshots before, I think there’s NTFS and ext (Linux) support in Haiku, but I haven’t seen UFS support in there. I could, of course, be wrong and admit to it. Also, as far as mounting BFS in *BSDs, I confess ignorance to this, too – I have never checked if this could be done or not, either. Others here will probably have a better answer to the above than I do. (However, I do know that Linux handles BFS (or BeFS) partitions fine in recent kernels, and should have no problem opening and reading Haiku volumes.)
That said, you should be able to mount a flash drive or disk partition you use with Haiku inside qemu, and talk to it from there. Another solution would be to create a disk image using FAT32 or another universal format, read it from inside a Haiku VM on top of BSD, and then sync it back to the host filesystem as a workaround.
In any case, despite all that I don’t know, I hope this helps. Maybe searching StackOverflow or the like may have more answers for this. (And again, there are more knowledgeable people here that will most likely have a better answer than I’ve given.) Good luck.