While I don't own an HP-1 I've been reading up the past few hours and from what I have read if you purchase that "Extreme Upgrade" for that scanner it would allow you to get the digital data stream aka "a discriminator tap" from the USB cable for the purposes of feeding that towards some application on a computer for digital mode decoding that the scanner isn't capable of doing itself.
DMR/MOTOTRBO requires either DSD (the original older and original digital speech decoder) or DSD+ (the newest digital speech decoder app available) - they are not the same apps, or just different versions - they're more than likely not written by the same people (and unfortunately those persons have never revealed themselves for either program).
Having said that, it IS technically possible to use the HP-1 with said Extreme Upgrade and then the makeshift "discriminator tap" functionality to feed the output into DSD/DSD+ and do the decoding of the DMR/MOTOTRBO bitstream.
Unfortunately, you won't have much luck with following it if it's a trunked system since the HP-1 can't monitor DMR/MOTOTRBO or NXDN or most anything else by itself in any respects (control channels, whatever).
So while the answer is still no, the HP-1 cannot monitor DMR/MOTOTRBO or anything other than P25 Phase I (it might do X2-TDMA, I don't know, never cared to look into the HP-1 as something that I'd own personally), you can get a setup to monitor your local police department or whoever that's using DMR/MOTOTRBO, it's just a somewhat complicated rigamarole of items and spending a lot more money on top of what you probably already paid for the HP-1 itself.
Unless of course your local police or whoever has decided to encrypt the traffic and if that's the case then you and everyone in your area are just SOL for monitoring them.
Personally I'd say get a ~$20 RTL stick and use that since even with the HP-1 Extreme Upgrade
you'd still be relying on a computer to do the decoding of DMR/MOTOTRBO bitstreams and if you're willing to go that far, might as well get a "cheap USB TV tuner" and do more with it than the HP-1 does out of the box, for the most part.