I don't see a problem with that.
Whether it's a problem or not is probably just a personal perspective. For myself, if I know the single player part is only a small part of that mission, the feeling of incompleteness grows.
If I did a bunch of missions but knew that with each one the stuff I did was but a small part of it and there is more to do, but you can only do that through a different type of play (one that I have no intention of playing), that would lessen the game for me.
We'll see obviously.