Well I was a DISH dealer since day 1, & I NEVER recall such a thing on any receivers.
I do remember the A/O's back then were ONLY $2, so there really wasn't any incentive anyway for a discount. They then went up to $4, then $5.
What you might be thinking of, is that E* actually PAID the dealers (WHAT a concept) a bonus for each phone install. If they got the receivers ping back thru the phone, you got paid the bonus. The sub didn't see any difference.
You probably ran lines f/DP's, because you had to have them to use WebTV service...