Oh, right, that kind of zombie that exists only where the pseudo-science used to justify zombies is even more convoluted and ****ty than normal.
Fact: Zombies cannot get in the tank if you don't want them to. If there is no one in it, they will leave it alone. If there is, they will not be able to open it. At all.
Fact: Unless the zombie is someone who worked on the specific kind of tank you're using, at which point all intelligence is already gone, they won't know what the vital optics on a tank are (and since there are tiny slits in the front of most tanks used to fire and see out of, it doesn't matter)
Fact: An Abrahms tank can travel 265 miles on a single tank of gas. If you can't get somewhere to help get any errant zombies off, you're doing it wrong.
Fun Fact: An Abrahms tank can move at up to 70 mph (that I've seen) on a good highway. Zombies will fall off. Mythbusters has shown us this with much lower speeds and without a rotating turret.
The military base that gets overrun is overrun by bull**** and fiat.