Do you mean unlock the SIM slot to be able to use it with other SIM cards or to install a different, non-carrier specific firmware? The term is used for both, and actually the term isn't really used all that widely any more for either (that's why you're not getting responses). If you're talking about unlocking the SIM slot, there are tons of threads about unlocking the phone's the SIM slot in the forums here. But long story short, yes, it technically voids your warranty.
If you're talking about the software on the phone, replacing it isn't a simple process on the Droid Pro. First of all, there isn't a non-carrier branded version of the OS for the Droid Pro. You can't simply install a vanilla version of Android on there, because one doesn't [publicly] exist that will install properly to the Pro. You'd have to go the custom ROM route. There aren't many custom ROM options out there for the Pro (and what is there isn't fully stable or completely functional), so you're limited in what you can actually do. But to answer your question, yes, it does void your warranty. You'll have to root your phone first, which voids the warranty right there. And then you're installing an unapproved OS, so that just adds one more tick to the tally. Luckily there is a SBF available for the Droid Pro, so if you should ever need a warranty replacement, you can flash that (if your problem doesn't prevent you from doing so) and then you're good to go with a stock phone that looks to Verizon as though it just came out of the box (from a software perspective).