If I pour boiling water into a +/- 70 degree urinal do I risk cracking it?

You do run that risk... and it's a strong one.. I'd venture a guess that you are more likely to break it than not.

Is there a reason you want to do this?

Boiling water should NEVER be introduced to any part of a plumbing drainage system... can warp and soften plumbing materials and that can lead to leaks in obvious places and in hidden places!

China fixtures, like toilets and urinals are especially vulnerable to boiling water and can/will crack if introduced too quickly.

Why are you asking?

Mark