In general the answer is yes. Now read on.
The MAX9217/MAX9218 require the DE (Data Enable) signal to toggle at least every 20,000 PCLKs (in practice it toggles every line) for correct operation. If DE does not toggle, video will not be transmitted correctly.
During normal operation when DE is high video data is transmitted and when low control data (HS, VS, etc.) is transmitted. Therefore, the HS signal, which is high when video data is being transmitted, can usually be used instead of DE. See pages 9 and 10 of the MAX9217 datasheet for a more detailed explanation of how the MAX9217/MAX9218 transmit video and control data.
There is a restriction caused by the way these parts transition between control and video data. From 2 PCLKs before a rising edge of DE to 2 PCLKs after a falling edge of DE, control signals are not sampled and so the timing of any control signals, such as VS, needs to be checked to make sure there are no transitions during this period. This restriction also means that when HS is used instead of DE it should be connected to DE at both the serializer and deserializer and not to HS (where it would toggle during the restricted period and hence be ignored).