The different systems make a little difference but not that much of one. Both carry a lot of the main talkgroups such as statewides. As an example 3155 (WI) is carried on Brandmeister (BM) and DMR-MARC.
Talkgroups on BM can be static (created in the system and permanent) or they can be dynamic (made on the fly). So, if the repeater allows it, you and a buddy can use TG 123456 temporarily on a repeater one day. Once again this is only if the repeater allows it, however on gateways (hotspots) you can create them to talk across the network. Example: You and John Doe both have DVMegas or OpenSPOTS and you both use 123456 it will go across the network to each other but not anyone else.
Hope this clears things up a little bit but I will be honest with you...play around with them. For me I actually have the Hytera NA TG which is heavily used in Vegas. So just program and play around with them and it might take a few times and reprogramming.
Hope this helps and does not hinder.