Yes, you can drill through wet wall panels. This is the best way to hang mirrors, cabinets, or anything else once you've installed your bathroom wall panels.
There are a few considerations before you start drilling into your panels though:
1. You need the adhesive to dry for at least 24 hours, and preferably 48 hours, before you start drilling. Do not drill into them right after you've installed them - that could cause the panels to shift and other issues.
2. You need to consider mounting strength. PVC wall panels are hollow inside and can crack if you hang things on them without the proper support. You will want to use wall anchors and distribute the weight evenly. If you are hanging something heavy, you will want to find studs to drill into with longer screws.
3. You need to consider waterproofing. Drilling a hole into your panels can cause leakage and water to get through, which you absolutely don't want. Think twice about drilling holes in shower areas and consider a non-drilling solution.
4. You need to consider electrical hazards. When drilling through walls there is a chance you could hit an electrical wire. Always know where your wires run and talk to an expert if you're not sure.
Once you've taken all of these things into consideration, feel free to drill through your panels. Make sure that you're planning on permanently having the drill holes there though, otherwise you will need to patch the holes and it won't look like new anymore.