The warm air that's coming from the fan blowing air into the radiator should be going in outside direction. But I agree with Rubix on the matter that the air pressure in your case is more smoke than anything. Unless your case is so restrictive in term of ventilation, it's not really a big of a concern.
I actually have front radiator fans in my set up blowing air going in the inside in a push & pull configuration. I did this hence I want to show the LED lightning effect of the fan. If I do the other way around, the LED lightning effect doesn't show. The reservoir can heat up quiet a bet (you can feel it if you touch it) but the warm air coming from the radiator is not really that warm to cause a concern even at high overclocks.