Willo's Dead Zone ability is very effective against 'local healing' this includes grovers healing, Grohk's totem and similar things. Dead zone will prevent deployables from being effective and will force champions like Grover to move out of the zone.
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.
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.
Unlike most front liners and supports grover has very good long range pressure. He can use his bonus damage scaling legendary to harass enemy front liners from long range or long range enemies from the objective easily.
Viktor's ultimate is reliant on him having direct vision of you so moving out of sight behind a corner or using opaque deployables(such as Inara's wall) will prevent him from selecting your location.