Pc/Playstation Account

[Starman]

Looking around the PSU Support Section it does seem that you would be able to play on both platforms with the same License. But I personally would contact Sega directly to confirm this.

To quote some of the info I found -

Can I use my GUARDIANS License for both Xbox and PS2/PC?
Your GUARDIANS License will be uniquely tied to the Game ID you used to initially purchase it, and cannot be shifted to a new Game ID, or to a Gamer Tag. However, there are benefits to having your GUARDIANS License uniquely tied to your Game ID. This means all your character data is saved on our servers, so you'll be able to carry your Game ID information on a memory card, and plug and play that baby at your friend's house, your friend's friend's house, or even a random stranger's house! (Note: We cannot be held responsible for you breaking and entering some random guy's house to test this out!)

What is a Game ID? Is it interchangeable with a Gamer Tag?
The Game ID is for PC and PS2 users. You can grab one from PlaySega.com, and use it to play on both the PC and PS2. PSO BB users can also use their old Game ID to purchase a GUARDIANS License.

Gamer Tags are created when you set up your Xbox Live account. Both Silver and Gold Xbox Live accounts can purchase a GUARDIANS License.

ATTENTION Please note, though, that PC/PS2 users cannot use their GUARDIANS License on Xbox 360 accounts, and you cannot use a Gamer Tag with your PS2/PC account.