Well, yes/no/maybe. 'Quad', in the module database, refers to modules that have four identical (more or less) functions, as a rule. There's a few things that actually are four-channel devices...but not many. Now, as to the yes/no/maybe part...let's say you have a quad VCO, such as Doepfer's latest unit. You could then feed each VCO into each filter on a quad VCF, like Qu-bits, and so on. But that wouldn't quite fit the bill of the reason for having modular, which is to take advantage of the open architecture to construct your own instrumental paths.
Example: with two quad VCOs, then you have two VCOs per voice, which you can deploy as 1-1-1-1 / 1-1-1-1 OR 2-2 / 2-2. More quad filters means more possible timbral combinations. So, yes...quad tends to refer to modules that 'play nice' in a 4-voice polyphonic environment and are convenient for that sort of architecture, but by no means do you have to use them as discrete voice components. It's just handier to patch polyphonically with them.