Is it possible to use a BJJ uniform for Judo practice?

In practice, sure. In competition, it depends on the cut and color of the uniform and what patches are on it.

Please see this link for competition approved gi guidelines.

http://www.teamusa.org/USA-Judo/Athletes/International-Federation/Guidance-for-IJF-approved-judogi

Wow. That's a lot of rules.

In a sense, a BJJ gi is just a judo gi with a more conservative cut, as to give opponents less material to grab onto. So long as you are within regulations, a BJJ gi will work fine for judo.

Yes, as long as you don't look like a nascar driver....

Totally fine. In the early days of BJJ in the States use of a judo gi was common. van is correct, it's largely just a more conservative cut.