I believe I would need some port information from you to answer this question best but from what I understand they do not use the same ports and I do not see any warnings with regards to this type of implementation. The existing Exchange - ERG configuration should not be a problem. The only warning that was present is to not have the MobiControl server on the same machine as the app server. Either way I am seeking additional information with regards to this for you.
I will include a couple of links below that may help you with your implementation of Soti Surf/ERG and Exchange.
Soti App Server
Technical Support | SOTI Inc. |1.905.624.9828 | email@example.com | www.soti.net |