I agree with 65GTO. Compressors are not an explosion hazard unless they had an excess amount of oil built up inside. Even at that it would take some time for the thing to blow if it is depleted of air and that much oil would be from a VERY old tank.
Make sure the tank has no pressure in it at all cut a square in the area of the hole that is large enough to put a small angle mirror into it and do a little inspection of the rust area. Cut a square into solid metal on the tank and use some 16 gauge plate and make an overlay patch. Do a solid stitch weld that is air tight and you should be good. I used to have to do this to a whole bunch of field tanks and never had a problem. People always get a little freaked out with compressor tanks but when they are empty they are just a metal ball. Just need to make sure nobody used it for a fuel tank!! Then you would have issues!
Good luck. Easy fix.