OTC is fine - its part of the TA and you can do as much (or as little) as you want. I went regularly, did lots of mil stuff and got an HGV licence too - you can (could then) even get a TA commission. The mil related stuff all helped no end at IOT - square bashing, bulling boots, knots and lashings, weapon drills etc. All counts as military service, there was a UAS in the same uni/city but there was no suggestion that I should have gone there. In fact any commitment to a club or activity is (was) seen as a positive factor.