I was reading on a few sites that because of the stereo input players are using these amps for bass. Is this safe to do with a guitar amp?

If your question is whether it's okay to use a guitar amp with bass, it's a matter of speaker capacity. But there'd be no reason why you couldn't use these heads to power some bass-capable bottoms. The EQ voicing would be a bit off from a normal bass amp but then, all of our basses that have stereo output are brighter than most other basses, so it might be a plus.