AFAIK there should be no real issue with MS access database files stored and edited on WHS shares since the release of PowerPack 1, even though it's officially not a supported scenario. If you have personal experience or (recent) links to examples of
problems with MS Access databases on WHS please let me know.
If for some reason you don't trust the WHS shared folders for storage of the MS Access database file you can create a separate share on a disk which is outside the WHS storage pool (from the server desktop).
MS Access files on a client PC which is backed up should be fine. WHS backup doesn't even know it's an MS Access file, all it does is back up (changed) clusters, not files. More details on WHS backup in
Home Computer Backup and Restore.