Is peroxide okay for cleaning if ear tubes?

No. Do not use peroxide in an ear with tubes or a perforation. If the peroxide goes through the tube it will cause significant discomfort.
In the right setting. If you have a lot of drainage coming from you ears (to the point that drops can't get to the tube to work for infection) or if your tube is plugged with some dried mucous, hydrogen peroxide can really help to clear a path. I wouldn't use peroxide for regular maintenance cleaning of the ears, but for the other reasons above I have never seen it cause problems and indeed it can really help.