I use bobb's and never encoutered a problem so far.
I don't know about that exactly, since I never used bobbtmanns Sath, but I had initially planned to have bobbs model alongside Rga's. But before preparing the guide, I pm'd Zacam over the issue of a packaged VP vs. a guide... and among that discussion, the case of two HTL's (the Sathanas being the only example) of the same model but by different authors... This is what he had to say...
2: As to the HTL Sathanas, we cannot release Bob's in the MediaVPs as it does not retain Retail compatibility for the placement of several of the turrets and subsystems, and is modeled in such a way that it cannot be made compatible.
And also, since this guide is more oriented towards the new, inexperienced user, I figured that it'd be safer to not get them confused...
However, I you all say so, I'll put up bobbs Sath as well!
IIRC, there's an issue with multiplayer games if turrets (or subsystems etc) are different on the client and server (and I can't imagine there wouldn't be). A few MVP models already cause issues, and the only way around it is to have everyone playing with the MVPs or everyone playing without them.
Not sure if there are other issues that show up in SP as well, but I don't know of any FS2 missions built around the exact locations of Sath turrets. The Sath is prominent in A Monster In The Mist, Bearbaiting, and High Noon, all of which I think can work with minor changes in turret placement.
We apparently gave some leeway to the Deimos, as one of the pairs of the rear turrets is a few meters displaced in the MVP model compared to retail, but that seems fairly minor. If bobb's sath has some more significant changes (very displaced turrets, different turrets, etc), it could affect any other mod that uses the Sath, no only the retail campaign.
Also, in terms of balance, bearbaiting is substantially easier with either model, since the forward flak guns are no longer semi-invulnerable. In the retail model, the centers of the turrets weren't actually inside the hull, which meant that trebs (and any aspect missiles) detonated uselessly in front of the turrets. It used to be nigh impossible to kill those flak guns before you lost half/all your wingmen. I believe both Rga and bobb fixed this issue in their respective saths.