8mm camcorders can only record onto 8mm tapes.
Hi8 camcorders can typically record on both 8mm and Hi8 tapes. When you record onto a 8mm tape using a Hi8 camcorder you will only get regular 8mm quality video so it is in your best interest to purchase Hi8 tapes for your camcorder.
To get digital quality video with a Digital 8 camcorder you will need to use Digital 8 tapes. Many lower end Digital 8 camcorders will only let you record and playback Digital 8 tapes. Some higher end models will allow playback of Hi8 and 8mm, but you will still need a Digital 8 tape for recording.