Sure, you have some options.

* Run NFS on a Linux system, XFS/JFS filesystem, export it to clients.
* Use a different filesystem, OpenBSD supports FFS/FFS2, EXT2(..3
without journals), ISO9660, FAT(12/16/32), r/o support of NTFS, and
network filesystems (NFS/AFS/Arla).

Finally,

* Port said filesystem to OpenBSD natively, baring license problems,
create your own implementation.

Does that help? if not, then, nope, sorry.
-Bryan.