Yes, and yes it is.

Seat tube failures are comparatively rare, and if/when they happen carry a low risk of causing a crash. The most likely result of a seat tube failure this low is inconvenience because you won't be able to put much weight onto the pedals, but the bike can still be ridden gently on level ground.

My personal record for riding a frame with a severed seat tube is about 20 miles in rolling terrain. Rode the flats and descents, but climbing was out of the question. So it crimped my style for a while until I got to where I could buy stuff and improvise a fix.