Must OFDM signal be time-division in a multiple-transmitter and SFN system when the signal is free of spread-spectrum?
In a multi-user scenario where every transmitter uses the same center frequency and bandwidth, but transmits different data, time-division multiplex has to be applied. Otherwise, interference between the multiple transmit signals will make successful reconstruction of a specific transmit signal at the receiver virtually impossible.

However, in typical SFNs, all transmitters are part of a broadcast network and transmit identical data. Examples are Digital Audio Broadcast (DAB) and terrestrial Digital Video Broadcast (DVB-T). In such networks, the guard interval of OFDM symbols can compensate for the propagation delay between different transmitters and there is no need for time-division multiplex.

Also, I don't think CDMA and OFDM can be combined. As a multiple-access scheme, OFDM(A) allows sharing of the same frequency band by frequency multiplex while CDMA applies code multiplex.