Yes, it always needs an orbiter to communicate with Earth.
The ExoMars Trace Gas Orbiter, part of the 2016 ExoMars mission, will support communications. The Rover Operations Control Centre (ROCC) will be located in Turin, Italy. The ROCC will monitor and control the ExoMars rover operations. Commands to the Rover will be transmitted through the Orbiter and the ESA space communications network operated at ESA's European Space Operations Centre (ESOC).
The plan is to use the ExoMars Trace Gas Orbiter as the relay.
NASA's participation in the 2016 ExoMars Trace Gas Orbiter includes two "Electra" telecommunication radios. Used successfully on NASA's Mars Reconnaissance Orbiter, Electra acts as a communications relay and navigation aid for Mars spacecraft. Electra's UHF radios support navigation, command, and data-return needs. 9)
TGO's Electra radios use a design from NASA/JPL with special features for relaying data from a rover or stationary lander to an orbiter passing overhead. Relay of information from Mars-surface craft to Mars orbiters, then from Mars orbit to Earth, enables receiving much more data from the surface missions than would otherwise be possible.
As an example of Electra capabilities, during a relay session between an Electra on the surface and one on an orbiter, the radios can maximize data volume by actively adjusting the data rate to be slower when the orbiter is near the horizon from the surface robot's perspective, faster when it is overhead.
Because TGO's radios are based on a NASA design, I suspect MRO could be used as a comms relay if needed. TGO has already been used as a relay for the NASA rovers on Mars.