I think the avalanche of jersey sales is for a variety of reasons, both to support Sam himself and to send a message to the NFL using the type of signal they understand, money. I'm sure a lot of people bought jerseys just to effectively have a memento for a small but historic event, and you'll surely see some of his jerseys in pride marches moving forward and rightly so.
The NFL itself has to be happy he was drafted, and the avalanche of jersey sales is a strong signal from the public they're happy he was drafted as well. Whether neophytes who know squat about the game voting with their wallets or more experienced viewers who can read the reports and know his odds are long and buying anyway. That sort of signal reinforces to the NFL and broadcasts to other sports what the public feels about openly gay players in "manly" sports.
Sam's jersey drawing big sales probably adds to his Q rating, making it more likely that marketing types seriously consider signing him up for endorsements. That's both good and bad, because his actual football talent may not be enough, so there's a real risk of that becoming a circus.
At the end of the day I think his route to a roster spot remains where it was pegged weeks ago, be a special teams demon, work hard, be smart. The depth at his position and his poor measurables at the combine just reinforces that.