It depends on how your VM is setup. VMWare workstation can do 3d rendering and run EQ (you have to change the mouse options to game mode other wise the cursor moves your camera way to fast).
I have ran games out of it through a VPN before to do essentially what you are talking about and mask it behind another IP and such. But I've never done it for just boxing in P99. I've done it for things like botting accounts in WoW and such.
If your VM is setup so that the connection to your network is bridged and not shared, nothing outside the VM should be aware that the packet is coming from the same NIC as your desktop really. The mac address on the VM will report as the virtual mac address.
That said, P99's anti cheat checks are really past the gray area and venture into the illegal territory IMO. But, there aren't enough players on there concerned about it to actually do anything about it. Their anti cheat stuff though will actually scan your computer and running programs and things like that and report it back to the server. The types of things no other gaming company can get away with without invasion of privacy suits and the like. There are some other things that P99 stuff does, there is a post about it on these forums somewhere but I don't recall where offhand. Anyway, point being, I would not be surprised if they have that anti cheat coded to detect a VM or VPN software and to flag you for a probable cheater due to that. And if you are flagged, they don't really care about proof over there on P99, they will just straight ban you.
I've been in a situation with them on it before, I bought plat, siphoned it through other characters on different IPs. Even used a good portion of the plat as burn plat to buy items and transfer to other accounts (running on yet different IPs) to make the trail to my main character less obvious. It didn't matter, they banned all the related accounts based purely on the trades. There were even some characters that weren't mine that got banned because of it, because I just gave away some items in the EC tunnel lol. They just assumed they were right and all parties were guilty, but they had no real proof of it.
Moral of the story, if you enjoy playing on P99, it's not worth the effort to cheat there. Best case scenario is you can get away with it initially, but if they ever suspect it and decide to take action, you are hosed no matter how well your tracks are covered.