Most but not all. Keep in mind that they accept one-way rentals from all over the country (especially warmer climes) where they may not always order the 4WD/AWD version of whatever SUV they are purchasing, so anyone who tells you that 100% of their fleet is 4WD/AWD is off-base. They will usually try to accommodate you if you ask though, and unless they are almost sold out and all they have left is 2WD models, you'll probably be fine.
Typically your chances are better with a Standard SUV vs. an Intermediate SUV and better still with a Standard Elite or Fullsize SUV, but with a Standard SUV reservation you could always pay to upgrade in a pinch if need be.