This is an extremely specific question: the odds of someone else here having the same iMac running OS 10.8, the same Sony TRV340 camcorder, and the same need to convert analog tapes with it are rather small. This is likely to be a case where you are just going to have to give it a try yourself, and report back here on your success or failure. Try to buy the camcorder from a seller who takes returns, so you can get your money back if the setup fails.
Somebody always has to be the first, right? This time, you're "it."
Regarding Lion, its a gigantic PITA "upgrade" that pretty much killed Mac compatibility with everything that had previously worked: hardware and software. If you know someone who tried this with the previous, more-compatible OS 10.5 or 10.6, and it didn't work for them, it is almost 100% guaranteed it will not work with Lion 10.7 or 10.8.
Aside from the "Lion" fiasco, Mac and Windows connection to camcorders is often similar. The video software and hardware is usually optimized to control and import from camcorders loaded with digital tapes or SD cards. When used as pass-thru to digitize external VCR input, or to digitize analog 8mm tapes on the fly, the camera communication with the computer may not be as dependable or useful.