This is an interesting statement. I'm curious what, beside the fact that he's playing on that line, suggests to you that it's a deliberate mentor situation? Serious question.
I just think if I'm Oates and I can't in good conscience award Tom Wilson a 2nd or 3rd line role, the next best thing to do is to give him at least one option on his line that should, in theory, give him some solid support. Of the possible left wing options, Erat is the most experienced, plays a hard, complete game, has the hands and size to help win board battles and act as a distributor in the grinding game and the skating to gain the zone with possession and create off the rush. Every other LW on the roster is better suited to support an offensive play than act as its catalyst, so to take full advantage of his 9 freebie games, I give him the best possible offensive option short of throwing him in the top 6, and I get to do so without disturbing my other big experiment (Fehr at Center, who at least gets the safety blanket of two linemates that work phenomenally together).
Since those two evaluations shouldn't be allowed to interfere with one another, Wilson can't play the 3rd line, but shouldn't be put in a situation in which his best feasible linemate turns out to be Chimera (presumes Erat to top 6, and subsequent displacement of Laich and the 3rd line), and possibly plays with Volpatti and Beagle. I don't really like playing him on the 2nd RW either, because I'm of the opinion that Brouwer is a rhythm player who really needs reps to get going, and establishing early 2nd line chemistry between he and Grabovski, especially if there's a mandate to make him a bonafide trigger man, is important to improving my team's poor 5 on 5 play.
To me, with a roster that has this many positions in flux, this combination of the 9 game deadline to make rookie decisions and the idea that if I have to experiment I'd rather do it early than late lead me to believe that by November, I don't think you see Erat in the bottom 6, the only caveat being that if Wilson gets pulled up from the 4th line, Erat could follow (probably prefaced by Fehr vacating 3C, and Erat either getting his shot at center, or flanking Laich with Wilson on the other side). That gets a little dicey, unless you want Fehr playing 1LW (which I like, since I've enjoyed Fehr on Ovechkin's line, but puts him on his off-hand), since I think things work out like:
Fehr-Backstrom-Ovechkin
Johansson-Grabovski-Brouwer
Erat-Laich-Wilson
Chimera-Beagle-Ward
I don't think that's the most effective use of manpower, it's just the only way I see Erat maintaining any permanence in the bottom 6. Besides that, I think you get him on 1/2LW and he becomes almost everything that made Kozlov a good fit at 1RW, or becomes the tandem option for Grabovski that Laich once looked like and Brouwer may never be, but regrettably puts Fehr in a bad position to succeed, and Wilson doesn't stick.
Erat/Johansson-Backstrom-Ovechkin
Johansson/Erat-Grabovski-Brouwer
Chimera-Laich-Ward
Volpatti-Beagle-Fehr
Maybe it is just optimism blanketed by rationalization, but I've seen Erat too often in Nashville to think that this is the best you're going to get out of him, and I have too much faith in Oates' ability to see talent when it's staring him in the face to believe that he doesn't see anything in Erat other than a 4th line option. It's the only scenario that makes sense to me.