As long as the service is generally from the same direction or tower; then the answer is probably ... yes.
However to provide isolation between the two modems, a splitter combiner is required for each antenna feed.
- A good cavity combiner/ splitter will add a 3dB loss from the antenna to each modem in the receive direction, however the transmit direction is more or less lossless. It also provides ~27dB of isolation between the two modems such that when one modem is transmitting, the spurious signal received by the other modem is dropped by 27dB, hopefully enough for both modems to operate successfully in tandem.
- Always use high quality low loss coaxial cable and make the connection between the antenna and the modem as short as practically possible.
- A MIMO antenna would require two splitter combiners.