...What would happen if you did format the drive would it not behave like an external USB hts+ journaled drive??
The problem will be, as I understand it, that HFS is not a native file system for Linux (which uses ext2, ext3 etc.). So, although there are hacks/extensions so that Linux can read a HFS formatted volume, it can't run on it. On the NAs I have, the internal file system must be ext3; it can natively format an external volume as ext3, NTFS or FAT, but not HFS.
Think if it in a similar way to OS X: a Mac can read a FAT volume natively, and can read NTFS with certain modifications, but the boot volume needs to be HFS.
I've probably over-simplified that explanation, and I stand to be corrected on the technical details anyway, but I think the above is reasonably accurate in layman's terms.
However - if the OP wants a way to have an HFS volume on a NAS, then the best way is probably to create a disk image of a suitable size on the Mac, transfer it on to the NAS, and then mount it remotely. I'm not sure how/if journalling works on such a disk image, though.