Yup, usually tires with LT rating have extra ply(s) on the sidewall making it more resistant to puncture and just more rugged overall. It also tend to give a better load capacity than a similarly sized P rated tire.

I've been told by tire shops that the X is rated as a "light truck." That being said, you can still put P rated tires on the X. The tires won't suddenly explode if you hit a bump or something. You just may be more susceptible to getting a puncture if you go offroading on trails with a lot of jagged rocks and boulders.