Check at the start of the match if Grover has the legendary card which gives him the ability to root with crippling axe, if he does then but the item to reduce CC duration, this can save your life many times during a match.
Grover's ultimate does not make him CC immune but stunning him will not cancel the aoe heal. Displacement heavy comps are very powerful against him since they can keep him away from his team and reduce his healing.