Ask for the view. The more general your request, the more likely you are to receive it.
If you ask for a particular room and it is occupied when you check in, there really isn't any way for the room assigners to know why you wanted that room.
Doesn't hurt to politely ask for your pool view again at check in. It appears that those who check in early in the day are more likely to be granted requests than those who check in later.