We recommend BitLocker, actually. It's baked into windows, and works seamlessly with the system. Additionally, the "Automatical unlock" option works very well with the pool.
However, a lot of people do not trust BitLocker.
And TrueCrypt, it's forks and a few other encryption solutions bypass the VDS system altogether. Since that is a big part of DrivePool... they don't work. And would require a nearly complete rewrite of the code JUST to support these products.
I'm not trying to start a debate, but just stating this and explaining why we don't support them.