From browsing threads for other HTC devices (though the official bootloader unlock is generally not the best solution) and reading documentation on HTCdev my understanding is that with the official unlock you'll be able to fastboot flash a custom recovery, which means that rooting is possible.
If you read the guide to rooting with Revolutionary in this forum (linked in the All Things Root Guide sticky post) you'll see that the procedure there is:
* the first few stages are about setting up software on your computer
* then you use Revolutionary to gain S-Off
* then you flash a custom recovery
* then you use the custom recovery to flash a patch to your ROM which roots it
Now I think it very unlikely that you can use revolutionary with that hboot. But if the official bootloader unlock lets you flash a custom recovery, then you do that instead of the revolutionary stage, and the later bits (which actually let you root/flash ROMs) are the same as in that guide.
As for the actual bootloader unlock, bear in mind that I've not done this. I've followed the steps on HTCdev as far as it would let me though.
* Log in to HTCdev.com (you have to register to get to the bootloader unlock instructions)
* It will tell you to download a software update and apply it. I'd skip past that bit, because I think you already have the right software, and if you apply their update it will wipe the phone.
* It tells you how to set up fastboot and adb on your PC (instructions for this are also in the Revolutionary guide here)
* It tells you to use fastboot to get some information, which it then asks you to submit before you can go any further. So this is as far as I've been able to follow it.
* The next steps will involve using this information to unlock the bootloader.
* Once you've done that you can flash recovery and root as described in the revolutionary guide.
Now a warning: reading instructions for this for a couple of devices, it seems that the HTC bootloader unlock will wipe the device anyway. So you want to back up whatever information you can before doing this. This is, unfortunately, another way in which HTCdev is inferior to community tools (so may be worth asking revolutionary anyway, though I think I know the answer).
There's a guide to doing this for a different device
here. Note however that as it is a different device you shouldn't download software from that guide, just use it as a description of the general procedure.
If at all unsure, ask before proceding. If I'm not around, Scotty who wrote the guide I just linked is a HTC device expert.