Yes it is possible. There is the "slight" problem that windows 64 bit drivers only work when properly signed by a microsoft provided certificate. And that is NOT free.
There's also the slight problem that for 16 and 32 bit drivers you need an external MS linker to obtain a working driver.
And YES, you are limited to the DDK provided framework, although that is not really an issue because there are Pascal translations out there.
You will also need to be able to strip system.pas into a very low-weight one, because as-is, you can't use system.pas in a driver.
That takes a whole lot of knowledge about FPC internals anyway.
It is definitely not for beginners, not even for intermediate programmers, not even for GOOD Object Pascal programmers.
It is also a bit pointless, because most people that CAN write a driver in Object Pascal will probably do it in C anyway.
Unless you are nuts, like me
If it CAN be done, we give it a try