I have an Ooma setup and a Brother MFC attached to it. There has never been a problem for incoming fax, but you may have to use *96, *97, or *98 and then the 10 digit telephone number when sending outgoing fax.
It was trial/error with mine; I ended up using *96. It depends on the amount of "noise" you have on your lines.
Thanks for the tip, will try!