Should my rooster be eating "Laying" pellets?

Excess calcium leads to issues in non-laying birds (males, females that are too old, too young, broody or molting) - specifically it can cause kidney damage (and other issues). How much impact it will have on a specific bird is not something one can predict, but the fact is that a bird that is not producing egg shells to expend that calcium, it is going to be stored in their body and lead to an imbalance compared to what the bird needs to live it's longest, healthiest life.
For mixed flocks an alternative feeding program is to offer a starter/grower ration to all the birds and then keep oyster shell available at all times for those birds who need the calcium for laying to take as they want. Another advantage of this approach is that layer ration tends to be on the low side for protein content - starter/grower rations are higher in protein.

 

No he shouldn't and a 15% finisher feed is nearly ideal for roosters.
The problem is finding a way if they're together.

For roosters, excess calcium can cause renal failure and visceral gout, excess protein can cause articular gout.
Excess calcium also affects fertility.

http://www.thepoultrysite.com/articles/2337/urolithiasis-in-male-broiler-breeders

Ol Grey Mare's advice is sound.
Another thing I'm considering is elevating a feeder only the roosters can reach.

 

Unless they are housed entirely separately there is no way to feed just this feed to this bird and that feed to that bird.

 

Other than layer feed, it would be the same as other chickens.
Also, like I said, roosters are better off with lower protein diets.

 

So this is a different rooster from your other thread? Because in that thread it sounds like they are together - ie the aggressive treatment of the hens by him.