I can't imagine the Army wishing to retain the services of a convicted paedophile whether he receives a custodial sentence or not. I suppose that it also depends on the case and any mitigating factors which come into play. That having been said a conviction and entry on the Sex Offenders' Register is likely to restrict which countries will allow his entry which would affect his employablity by the Army.
As he has admitted guilt, he should automatically go on the sex offenders register no matter what the sentence. and as there are soldiers serving under the age of 18. They are officially classed as juniors. It must be illegal for someone like him in a position of authority to possibly be in charge of juniors. So if they is any justice he should be dishonourably discharged from the service.