If you absolutely need an SUV or crossover, you should reserve one. If you're OK with hoping for an SUV, being pleasantly surprised if there is one, and OK if all that's there are full size sedans, then it may be worth gambling, especially if SUV rates are high.

I wouldn't expect the location to accommodate a request to save you a particular type of vehicle that's above and beyond a full size in ES. And as a fellow Exec member, I wouldn't be too pleased if I couldn't take a vehicle parked in ES because it was unofficially "reserved" for someone else...that would drive me to call ahead as well, and you could see how that could quickly spiral out of control.