Well, as has been pointed out, there are people in the WWE HOF who aren't what most will think of as genuine "all time greats." However, if the HOF was only for those that most WWE fans would think of as the very greatest of the great, then there really aren't many more names to be added anyhow. Savage is going in this year, Hogan's been in for 10 years, Sammartino's been inducted, Buddy Rogers, Ric Flair, Shawn Michaels, Andre, Harley Race, Roddy Piper, Bret Hart, Dusty Rhodes, etc. Of the wrestlers that most would probably view as being an "all time great", the handful that are yet to be inducted include Lou Thesz, The Rock, The Undertaker and a couple of others. If you're someone who believes that only THE very top guys should be in the HOF, you might as well just close it off once those last few names are added.
For someone to have a HOF career, in my eyes, they've had to deliver meaningful contributions to WWE and/or pro wrestling in general as well as being genuinely memorable, mostly in a positive way. In the case of Owen Hart, while I do believe that some fans have definitely overblown or overhyped his career since his death, particularly considering how tragic and unexpected it was, he was also someone who had a memorable career. While some of his career success did stem from the fact that he was Bret Hart's little brother, Owen Hart was a very solid and consistent part of WWE's mid-card, tag team and upper mid-card picture and participated in a number of memorable feuds and matches for most of his time in WWE.
As someone else mentioned, here we are today nearly 16 years after his death still talking about him. As I alluded to, his death was tragic and unexpected, he was only about 3 weeks into his 34th birthday, but his death wouldn't have had such a major impact if he wasn't popular not only with the boys & girls in the locker room, but with fans as well. The memorial show held the night after he died, the May 24, 1999 episode of Raw, titled "Raw is Owen" was the 3rd most watched episode of Raw in history. I still remember how utterly devastated Jeff Jarrett was when giving his interview, he was extremely close with Owen and they'd won the tag team titles together early in '99 and he was so torn up and sobbing so hard that he could barely string two words together at times.
As I said earlier, I do think that Owen's career and greatness has been exaggerated to some degree by fans due in part to nostalgia and the fact that Owen is still looked at as one of the ultimate "What if?" scenarios. Like I said, he was only 34 and he potentially had a lot of years left in wrestling.
As far as Owen going into the HOF by himself instead of simply as a member of the Hart Family, it's unlikely to happen anytime soon. Owen's wife Martha is still extremely, extremely bitter towards WWE and would probably raise all kinds of hell if word ever got out WWE was even considering inducting him by himself. Not that I think she's wrong for still feeling angry, but I do think it's a bit misplaced. For instance, not too long after Bret Hart resumed a relationship with WWE back in 2010, she sued WWE for using photos and footage of Owen as part of a Hart Family DVD compilation, she's railed against any member of the family that's had anything to do with WWE, she even sued her sister in law Diana Hart for a book she wrote back in 2001. While I think Owen deserves to be in the HOF himself, I doubt it's worth it to WWE considering the shit storm that Martha would cause.