You can not use standard nails for PT wood, the ACQ presevative (Alkaline Copper Quaternary) will break down the nails.
You can buy nail gun nails for ACQ wood, it will say it right in the label.
Also the nails you use to install the PT to the floor must be ACQ rated, hot dipped galvinized or stailess steel.
Either way of nailing is ok, some inspector prefer toe nails because they can see that the nails have been installed properly.
Also if you are toe nailing #8 or 10's are fine, you don't need 12's