Like any of the other home screen replacements, Launcher Pro runs on top of the stock GUI. It does not actually replace it.
Hence, anything running within Sense will continue to run if using LPP.
I just got the TB after using the Moto Droid (original) for almost 2 years. With the Moto Droid, if you wanted it to run smoothly when using another home screen replacement, it was recommended to delete all widgets, etc on the stock home screen, then run whatever replacement you wanted.
Again, this is because such replacements run on top of the stock. So if you have widgets running on the stock home screen and on the replacement home screen, you are running duplicate widgets, using twice as many resources.
I installed LP on top of Sense and noticed no significant decline in performance. It clearly has a better processor than my moto droid which explains a lot