Is it possible to have a weak pull-up with a push-pull configuration?
Are there any benefits to doing so?

 

Well sure. If you turn off both halves of a complementary output, you have an input with a weak pullup. Seems like the standard port configuration for an Atmel part,

 

Thanks!

 

Is an input with a weak pull needed only when you drive it with an open drain configuration?
(i.e. if the input signal was driven by a push-pull, would you still need a pull-up on the input pin?)

 

if you allways drive an input pin with a push-pull output, and both devices are allways on at the same time, then the pullup is not needed and just wastes power.
Weak pullups allow for only very slow signals, but consume very little power. For higher speeds you would usually need a stronger pullup outside the chip.

 

Thanks!