I know you said you had one clown, I was just using my pair as an example.
It's certainly a risk, and just in my opinion, I think the clown will eventually find its way over to the elegance. If finding a new home for the fish is not an option, then you may have to be prepared to find one for the elegance.
Again, this is my experience and my opinion only, you may be luckier than me! I thought I was in the clear as the fish and elegance lived happily on opposite sides of the tank for a year. Then one day...
Just from my reading on this forum, if your clown does decide to take up residence in the elegance, it could almost certainly spell out destruction for the coral. For the price you'd pay for a healthy elegance, I wouldn't risk it.
I doubt a hawk/blenny would go in an elegance. My fish stay clear of it, they do have a potent sting. Could the elegance catch one of them if they swam through it? Probably not, they don't work quite like anemones. Then again, my elegance eats snails like there's no tomorrow...