I believe 2 is "supposed" to be what the ULA implies. But I agree with Brian in that, as long as its not being abused im sure they aren't going to send the DAW police to your house and break your door down using the VST battering Ram.
The most I've ever used it on (needed) was 2 but I can see some cases where 3 would be needed (2 home / 1 mobile unit).
Cakewalk really is cool with its clients. Its good to know that company's out there trust their customers to a certain degree. that's hard to find these days.