I can't see anyway in which the velocity with which you are playing the keys can have any effect whilst using the arp.  You can have a nice patch with velocity affecting the filter cutoff as you want it but, when switching to the arp, the velocity you use whilst playing has no affect on the audio that Z3TA+2 produces.  I remember using one VSTi which let you mix between the velocity level programmed into the arp pattern and the velocity level being played by the user.  You could then have it so that only the velocity you played had any affect and the programmed velocity levels in the arp were ignored.  Or the velocity you played was ignored and only the programmed velocity levels in the arp were used.   Or you could set the ratio anywhere between the velocity you play and the velocity levels programmed into the arp pattern.  I haven't really used the arp much because of this and the fact that creating your own seems to be longwinded and uninspirational.  Just a simple step sequencer with note pitch, length and velocity settings would do me really.