As for the question implied in the thread title, the termination resistors are part of the filter design. Omitting it changes the filter characteristic. A passive filter can be be designed with arbitrary termination on both ends, a resistive component is required at least at one end.
If your application is IF rather than baseband sampling, you don't need to observe the Nyquist criterion. A bandpass filter may be used, but it isn't necessarily required if the input signal is already band limited. But even if you don't have signal components at image frequencies there may be still noise power that can be suppressed by a band pass.