Historically the payout was less than 2%, so this is an amazing deal that probably won’t last. It’s worth it to make any Marriott (including Starwood) bookings through the site, and to make as many as you may need quickly. Indeed, making cancellable bookings that you may need can make good sense.
Since you’re sent from Ebates to Marriott’s own website you will of course earn elite credit and have elite status recognized, as well as earning Marriott points for your stay and availing yourself of their member rates.