a filter will filter any audio signal
the only thing to watch out for is that most non-modular signals will be significantly quieter than modular level - so you will want to amplify the input signal - there are dedicated input modules available or you could use a vca that catually amplifies the input - such as veils (or a clone as it is discontinued) which has over 20dB gain available per channel...
nb most vcas don't increase gain - so make sure if you go the vca route that you find one that has ample gain available
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities