No, he does not need an OBDII tool. This is a '95 Monte, the only year Monte that didn't have OBDII. If it's anything like my Honda, you need to put a paperclip or a wire in one of those connectors you mentioned. This will activate the check engine light codes. It will blink in a series of short and long flashes. For instance. 3 quick flashes and 4 long flashes would be a code 34. Then you google it.

Hot while sitting still could be a lot of things. Fans not working right, air in the coolant, tstat not working correctly. Regardless, you need to flush and bleed your coolant since it has oil in it.

When I had my 3.1 it would have a hard time starting when it was hot, but that was my MAF sensor's fault. You don't have a MAF on your car though, so it beats me. Check your sensors is about all I can say.

Good luck.