I saw it as a VERY unnecessary risk to chemistry. Sark appears to have had a ton of well respected coaches leave their comfortable gigs to head to Texas as assistants. For each of them, there was an articulable reason for them to do so.
Mike seemed to, at best, be a decent LB coach. Even that statement could be argued. I'm sure that Sark worked with him long enough at Bama to conclude that his abusive history is behind him. Obviously Sark himself understands burying the past and earning redemption.
However, it seemed like it was maximal risk, maximal bad blood, for only a chance of getting a good LB coach. The man hired in place of Stoops is recognized as an assistant DC, was being considered to replace PK at Washington, and likely would see HC offers this season. The pedigree is much more in line with the other coaching hires.
At least Sark now very much knows where the line is.