I agree with Krang in that if you traded for Hernandez you would want to get some sort of long term deal done because if not, you just target him in FA. Interesting that you bring his name up as his head coach in college was Sean Kugler.
Obviously at this stage you are trading a 6th or 7th pick for him just to tie him up and take him out of the FA market. No different that trading a 5th for Ertz with no deal beyond this year. But sure, I'd want an extension tied in to the trade.