Safe, yes, as neither will harm the other. Unfortunately, a Bluray disk will not play in anything short of a bluray drive. Put a BluRay disk into a DVD player and it will spit it out, or refuse to mount it saying "not able to recognize disk".
The BluRay disk requires a different laser. The name bluray is from the fact that it uses a special blue laser vs the standard red laser used in a DVD player.
The same goes for playing a DVD in a CD drive. A CD drive can not see a DVD, but a DVD drive can see a CD.