No, I think the GR55 is like the GR20 in that it can not be used as a standalone MIDI synth being triggered by external midi. The only thing that triggers the module’s inbuilt sounds is the hex guitar pickup that you fix to your guitar (or in the case of Godin guitars that comes built in to your guitar).
Thr GR55, like the GR20, will send midi information to e.g. a DAW or another synth module.
The difference between the GR55 and the GR20 is that the newer GR55 also uses the hex pickup for generating modelled sounds (i.e. no latency).
Steve.