It is perhaps easier to first say that a Sonos Home Theatre device - (Arc, Beam, Ray, Amp etc.) can only be ‘bonded’ to two rear left/right surrounds and a Sub (or two Subs in some cases). The HT devices all cater for the front left/right/center channels and no further devices can be added to that ‘bonded’ Sonos ‘room’.
The next thing to note, is that none of the Sonos portable/rechargeable battery products (Move, Move 2, Roam, Roan SL) can be used as part of a bonded HT setup - so no these (Roam) speakers cannot be used for Sonos rear surrounds, or indeed for front left/right channels.
Additional speakers however like Roams etc; can be ‘grouped’ with Sonos HT rooms. See this link on how to group/ungroup Sonos devices…
https://support.sonos.com/en-us/article/group-and-ungroup-rooms
Note: ‘Grouped’ and/or ‘Bonded’ Sonos rooms all play in perfect sync for music audio, but if playing TV audio to a grouped room, there is a ~75ms audio buffer delay to each and every grouped room, meaning that the grouped room, such as ‘Roams’ will not be in sync with the HT speakers, by default.
However there are tools in the Sonos App designed to buffer the TV HT audio to try to bring the HT room in sync with any grouped rooms - but that in-turn may introduce lip-sync issues with any video on screen. There are buffering options too to prevent audio dropouts across grouped rooms. To perhaps understand a little more about these Sonos tools, maybe see these Sonos support links:
https://support.sonos.com/en-us/article/tv-audio-and-video-are-out-of-sync
https://support.sonos.com/en-us/article/tv-audio-stops-or-skips
