How do I get a snare drum roll to play back with Groove Agent SE5? Surely there must be a sound sample for that, or isn’t there? I faintly remember having done that with Yamaha XG or something but ever since Dorico switched to Groove Agent as the default, and with this completely different UI, I’m totally at loss here. 
I’m not sure about Groove Agent, but I am quite certain there are rolls with Iconica Sketch and wuth the new Marching band sounds (F1 in groove Agent might sound artificial, if I believe what someone wrote about it)
I don’t have dorico open at the moment but when you go to the midi options in groove agent there are different rudiment options available. One of them is a roll, there is also a brush, flam and I think a few others. The problem is that these options can’t be turned on/off easily. So what I do is I create another snare drum with a roll and use that in a new percussion map. It’s a bit wonky, I think it should be worked on, but that’s the only way I have found to easily do this in groove agent.
I also use percussion variants with East West sample libraries which frankly sounds a lot better.
You can choose factory playback templates that do not use Groove Agent. In the playback templates dialogue, show all factory, then choose one that does not include GASE in the template description.