Posted: 12/10/2016 at 14:24
I'm not sure if your infiltrator is Cotoneaster lacteus, the leaves look a bit too short and wide to me, but it's definitely a cotoneaster of some sort.
As it's already taller than the hydrangea I think you can assume it will swamp it given a chance. You won't get flowers and berries if you keep cutting it back.
I don't think you can get the best from both shrubs without digging up both and pulling them apart.