A single vibe pump cannot service two groups. A vibe pump will give out 12-15 bar of pressure (depending upon spec) which can be reduced down to 9 bar with the use of an opv. But if we double the flow (using two groups at once) then the system pressure will drop - lets say by half (this isnt technically correct but close enough for this purpose) leaving you with a maximum of 6-8.5 bar at each group.
A rotary pump however is designed to keep the system pressure at the set point - meaning if one group or three are in operation each will receive 9bars of pressure.
You can replace a vibe pump with a rotary but I wouldnt consider replacing a rotary with a vibe (besides rotary pumps are easily serviceable - so the problem pump can probably be fixed)
Yes this is way over simplified but it is just to get the point over.