The guy has character concerns, but that's the Rams call to make. They have far more information than I do.
What I know about the guy is that he came up under Bill Callahan in the NFL (he was Callahan's OL Coach when Callahan was HC of the Raiders). If Bill Callahan wants you coaching his OLs, you're damn good at your job. After he left Callahan, his track record is outstanding.
Kromer became the Saints OL Coach in 2009. The Saints OL had zero first round picks. Four of the five starters were picked in the 4th or 5th rounds. The Saints OL had a combined zero Pro Bowls and zero All Pros at that point. Kromer coached the OL from 2009 to 2012 (4 years). In that time, the Saints OLs were selected to a combined 10 Pro Bowls and 5 All Pro teams.
He left the Saints to take the OC job with the Bears, whose OL improved leaps and bounds under Kromer (Kyle Long even made the Pro Bowl as a rookie). Following Trestman's firing, Kromer went to Buffalo. This year, in Buffalo, the Bills led the NFL with 2630 rushing yards, 29 rushing TDs, and 5.3 yards per carry (after leading the NFL in those categories in 2015 as well). Additionally, the Bills led the NFL in yards BEFORE contact on rushing plays.
Speaking strictly about football, he's one of the very best in the NFL at coaching OLs.
What's interesting to me is that Kromer runs a PBS. I've been uncertain whether McVay plans to run a PBS or ZBS with the Rams. If he hires Kromer, I'll have to assume that he plans to run a PBS.