As long as he can keep the temps the condenser is in below 100F (preferably below 90) he should be ok, but energy wise the unit will work harder to condense refrigerant and of course venting the heat with a secondary blower will use added power.
I have seen so many units installed this way burn up in a year or two so hopefully that doesn't become an issue. Definitely not ideal but when stealth is required you gotta do what you gotta do.