I also agree with Coach Regan.
Playing these players should be necessary, and it is also realistic, as role players are there to physically show younger players how to do stuff in addition to verbally coaching.
The experience gain that Regan suggested I have to objections too.
However, I do think that these players should give a small boost to the training of other players at there position, for their best skills.
(Ex, a physical defensive big man can help a defensively struggling rookie train his defense)
Since players can't will there skills into other players, the training boost they receive would have to be dependent upon several factors.
1. Potential of rookie
2. Xp of veteran
3. Skills (let's say a max of 3) that the veteran is able to pass along
4. (Maybe, not sure about this idea) time veteran and rookie play together
5. Veteran and rookie must play similar/same position (C/PF p, ect)
Now I am sure there are ways to make sure that this does not unbalance training, but if this is too hard to implement, then just an xp boost is fine,