No, those comments are highly discouraged through the SE network.
In fact, if a moderator sees them, we can delete them without notice (well, this is true for comments in general but especially here). Users can even flag those comments and I think they'll be deleted by pretty much every moderator.
The point is: the accept rate is meaningless. It's often taken as a seriousness-o-meter, but it really doesn't tell you anything else except how much a user accepted. It doesn't tell you why that user didn't accept in the first place, why do we assume it's because the OP is malicious? I have some "suspended" questions myself.
The OP should not be forced to accept, because that acceptance shows that a) it helped the OP and b) it's most likely the correct answer. If the existing answers don't satisfy one or both these points, why should the OP accept? I wouldn't accept myself! For the record, the accept rate is probably going to disappear from the public view, I think it'll still be available in the user profile, though.
So these comments do not serve any actual purpose except nagging the OP.
What you can do instead is tell a newbie how the system works. Like:
Hello xxx, I see you thanked this answerer. If this answer helped you solve the problem, you can accept it clicking on the tick (√) next to it.
That is different, you're helping someone using the tools, not "c'mon accept, c'mon, click on that". Note that if the OP accepts after this comment, you should delete it since it's obsolete.