An overspeed warning is an exceedance of set limits (Vmo / Mmo) and therefore should be reported in the Tech Log - that seems to be perfectly clear to everyone. That, of course, is only the follow up.
Remains the question: is there any need for concern when someone decides to descend in VS mode? It largely depends whether you have Auto Throttle to take care of (over-)speed problems. As most (all?) turboprops lack A/T systems, their pilots have 3 or 4 modes of descent at their disposal: Vertical Speed (VS), Indicated Air Speed (IAS), Basic Pitch and sometimes Vertical Navigation (VNAV).
VS mode: Fixed Rate of Descent. There is of course the airspeed indicator needle to monitor more closely as you have just given it permission to wander about its scale.
IAS mode: Fixed Air Speed. Vertical Speed now needs the extra monitoring, as either very low and very high descent rates are possible. The power levers (at least on "my" type of machinery) need a very delicate touch to make this a comfortable ride. Also, I have seen overspeed warnings with Vmo minus 5 programmed into the flight director.
Basic Pitch - both VS and IAS are on the loose here, so the amount of control over the aircrafts' path feels limited. Maybe just my feeling...?
VNAV - follow 'glide slope' type of FMS generated path in space. Both VS and IAS are let go of, but as VS is shown in the FMS monitoring is easy.
Personally (turbo prop jockey, too) I do not think that VS is a mode to be avoided, actually, I do it almost every time. My only other realistic option is VNAV. Just my two cents worth of course.....
