Did the guy on tenors say it was alright to use his tenors while he was gone? If he was fine with it, go ahead and use them. Personally I would just stick with my own drum. I wouldn't really want anyone using my drum if I was gone but thats just me. (plus I have the nicest drum )
Why was the snare player going to use the tenors? Its not even his instrument so I don't get why he would start playing them instead of you.

For those that didn't understand what I was saying (most, it's probably my fault for wording it that way), I meant neither of you should be playing on that instrument, considering it's not your setup.