Dad better take a chill pill. Baseball is a game of failure - so what if he got overheated, what does that have to do with performance on the field?
Just so you know (probably more important dad!) recruiters are looking at "tools" not actually statistical results. A player can rope 4 line drives and go 0 - 4 as a result and knowledgeable baseball coaches will see the skills if they are there.
If he is susceptible to heat just make sure he drinks plenty of liquids prior to the event and takes a wet towel with him to cool off between innings.
He will be fine and I would not worry about one outing. Remember it is a marathon not a sprint.
Good Luck!