Theoretically no. If more providers offered Sunday Ticket and it was offered for less as a result by those providers, the large bag of money they get for the NBC/CBS/FOX deals would be signifigantly smaller because ratings on networks would be worse, and the value of those contracts is based on the advertising money NBC/CBS/FOX can bring in as a result. The NFL won't be getting a billion/year from each provider, so hard to say the sum of all of the signed up providers will equal what they're getting from DirecTV as well.
There's no way to prove that one way or the other, it's hard to say they would make more or less, there are a lot of moving parts to it most of which we can only speculate about.
But as of right now...only a small portion of the cable/dish subscribers are getting ST. Would you figure that IF offered to MORE folks...MORE folks would buy it?