I'm assuming its only cracked and its still somewhat usable. In this case, you can go into the BIOS and figure out what resolution the screen is. Also, on the order details it would tell you this information as well. Anyway, no it doesn't matter if you replace the screen with one that has a different resolution. The only potential problem is that he might think text is too big or too small depending on if you get a screen with a smaller or larger resolution respectively. "True Life glossy" doesn't have anything to do with the resolution of the screen in general however.
True Life refers to Dell's particular marketing slogan for glossier and sharper screens. Every screen/computer manufacturer has some slogan like this.
Glossy just means the screen reflects more light and the images typically look richer (as opposed to matte)