Why not move the whole boot disk and Serve.app and the rest out to the RAID array? It's not like OS X is that big a hunk lately in comparison with the size of various RAID arrays, and relocating the whole configuration means you won't have to deal with a piecemeal relocation, nor any future upgrade weirdnesses that might arise from the relocation.
That approach aside, Mavericks Server storage is mostly under the /Library/Server path. I haven't tried relocating indidual hunks yet, either.
Ah, slightly misread... You could shut off Software Update entirely, and use Reposado. That'll let you do what you want.
The other hunk you'd probably want to move is the Caching Server.
The easy and official way is to relocate all services' data via Server.App -> Your Server -> Settings -> Service data location (or similar).
If you just want to change the data store of Software Update Server, you could try altering the string of "updatesDocRoot" in /Library/Server/Software Update/Config/swupd.plist. Don't forget to restart Software Update Service after your operation.
Hope that helps.
Thanks for all the suggestions guys! From that I was able to see where the main data lived (which was 92% Software Update) and I stopped the server, moved the data to the RAID, and created a symbolic link to it, checked permissions and restarted the Server. It's all good.
I'll probably move the entire Server over to the RAID having seen the posts about that after I'd already used the method above. But I need time to sit down and get it all tickity-boo.
I'll look at Reposado, I'll try that on my test bench with a few systems in my office, but not wishing to be too adventurous and probably going to stick with Apple properties.