In the past we've found that this doesn't work from the Crestron interface side of things. At least not at the outset of their partnership. From then, we've pretty much stuck to using ONE Port (source) to a distribution amp to get audio wherever it is wanted, and that worked well since grouping/synching issues sort of can't happen.

Is this still an OK way to do it, or can you group Sonos zones from outside of the actual Sonos app?

I don't believe there is a way to group sonos without using the sonos app. There hasn't been any additional integration control with the "partnership" since it happened.

Since Sonos has recently provided the firmware updates to use the S2 app all existing TSWs that you could direct load the sonos app has been broken (need to wait for the X70 panels) which really breaks the sonos/crestron "partnership".

You can do this with the Sonos modules (not the imbedded Sonos app). My issue howevever, is that this has been a dissapointing partnership. I have tried the integration in all it's forms and most clients are VERY dissatisfied with it because with every update comes the potential for it to be broken. I love Crestron but I do not think they are agile enough to keep up with changes to Sonos along with their own developments.