The handling agents for KLM in Glasgow are particular Nasties with regard to the "30 day" issue. I was almost denied boarding once until I pointed out that my trip WAS exactly 30 days as I didn't arrive until "tomorrow"
There could be an issue at the airport of departure if his return flight is not within the 15 day window of his VOA, it all depends on the check in staff, some are worse than others.
Yes, as long as you don't get apprehended at a passport check prior to reaching immigration. However, still a pretty stupid thing to do and could cause scrutiny on the next visit.