Going after JUCO guys is by no means "a sign of desperation" and it shouldn't "raise a red flag" either, because there are LOADS of hidden gems at that level.
Most of them are simply there because they didnt qualify academically but are oozing with talent, some are there because of character flaws (and those typically quit or get kicked off before even getting out of JUCO), and then there are the guys that go there because they need a second chance to improve in certain areas before they can garner serious attention from D1 schools (I needed a little more time to develop physically and fill out my frame, so I chose the JUCO route out of high school instead of going D1- AA or D2... every kid dreams to play in the SEC right?)
What they are looking for, and quite honestly they expect it, is a guy that has all the skills, size, and maturity to come in and be ready to play from day 1 and doesn't need to have his hand held leaving home for the first time like Freshman do.
No, Tennessee hasn't had the best of luck when going that route, but I would be willing to bet they go after/sign less JUCO guys than just about anybody else in the nation. Not sure for their reasoning, but it's always been that way.