Well, of those two, only the Optomix is a "true" LPG. It uses the vactrol design, which puts it into the same operational category as the original Buchla LPGs in that the decay aspects are going to have that "organic" envelope drop-off. Other versions that use a much faster/more responsive VCA+LPF combo (like the Dynamix) aren't going to have the blurring of contour that the vactrol designs tend to possess. So with those, you could easily shift to a VCA that's being fed via a lowpass VCF (or vice versa, if that works) controlled by similar envelopes...but you can't quite do a 1:1 replacement of a vactrol device like a LPG with that combo.
Another thing about the Codex Veils clone...you have that sweepable VCA response curve on it, which will offer you more flexibility than simply having either fixed linear or exponential responses. Very useful if you want a VCA to respond more or less aggressively, as the situation might dictate. Plus, if you want to break out VCA 1 on it, you can still mix the outs of VCAs 2-4, etc.