Well now that you said that the control medal is tech, I'm going to disagree with you Salkafar. I don't the g-units can reproduce because the g-unit is comprised of the bio-boost creature that is kept under control because of the control medal. Both of these entities make up the guyver. So while maybe the bio-boost creature can reproduce (I can't imagine how), without the control medal, its not a guyver.
My theory is, the bio-boost creature is a manipulated creature the creators either found or manufactured and they forcibly implanted the control medal onto it. I don't know if the creators would've wanted the g-unit to reproduce anyway. The g-unit is hardware for the creators and if said hardware was to fall into the wrong hands, and it was able to reproduce, if their enemies got a hold of it they could reproduce an army of guyvers.
I think the creators manufacture the bio-boost creatures in order to prevent this occurrence. Plus, they most likely had a way of issuing the units to trust-worthy people in order to prevent traitors from using the units.
At least this is what I think...