If the Roamio's moca is working, hopefully the Mini's moca will work too. The Verizon techs are usually good about making sure the coax is in good shape for moca, since most of their boxes use it.
Only point to note is that both boxes need to be fully activated for the Mini to accept the Roamio as a host. Typically takes up to 24 hours, but some have had to wait as long as 3 days for the Mini to fully activate for whatever reason.
If you run into a slow activation issue with the Mini, sometimes renaming the Roamio and then forcing it to connect to the service kind of wakes things up. After which point, reboot the Mini and try the Guided Setup again.
And sometimes it work right out of the box too. So who knows.