It depends. They can certainly be grouped in the Sonos software, but you can’t use the Sonos Roam as a surround speaker. And if the Era 100 is in use as a surround speaker, there will be a delay between the home theater ‘room’ and the Roam’s rooms of at least 75ms. 
 

I think Bruce is confused -or anticipating the next question -  don’t think you have a home theatre speaker (Arc/Beam/Ray) so yes, the Roams and Era can be grouped on wifi. 
 

Edited to add: Sorry - I just looked at @Olliedawg348’s profile so maybe Bruce was right to anticipate the surrounds question! Sorry Bruce

Lol, feel free to jump in anytime. I can make wrong assumptions with the best of them, or even leave out pertinent data because my mind is going in a different direction ;)

Thanks for the replies. We use our Beam upstairs strictly for our TV, nothing else. I get what Bruce is saying, but if we take the Beam out of the picture, will the Era 100/Roam solution work?

Yes, as a group. Set the Era as a new room, and then group with whatever else you want to play together. Room name is just a label to identify a speaker. 

Gotcha, nik9669a. Props to you and Bruce for making short work of this question.