Based on the TIMATIC data, he should be able to use the TWOV facility at FRA in both directions, as he has a valid UK visa and will be travelling to/from non-Schengen countries.
Ahh. I think I know what I was misinterpreting. I was reading the non-Schengen member state bit as "non-Schengen EU member state". I take it the more obvious interpretation was a non-Schengen state.