Yes you can breed polled to polled,BUT you want to be prepared to Cull.
There is a 25% chance you can get a Hermi with a Homozygous breeding.
If its a Heterozygous then its doable to get Polled does that go on to breed and produce.
I Have 2 Polled does that are Heterozygous and will be bred to a Horned Buck.Polled is dominate.
What type is he ?Look at the top of the head does he or she have knobs where horns should Be?If so then they are a Heter.
If the top of the head is smooth and no bumps then they are Homo and I would not Breed them.