Effect of filter ripple on OFDM
Assuming the ripple is slow (long in the frequency domain compared to the subcarriers), then the ripple can be an channel-dependent attenuation (or relative gain) which is easily ignored for phase-based (most modern) communication signals.  However, if it is fast (shorter in frequency than a subcarrier), then it will have a distorting affect on the received symbol and a more sophisticated equalizer may be needed.