In theory, steel is fine to shoot. In fact, most hard plinking targets are steel, and long-range targets are often the same. It's also a great way to test impact/penetration, and audibly lets you know when you hit.
As for a good idea - most of the time they are hung up, so when the round hits, it disperses the energy into the target, which "shakes" it off.
If the round were to ricochet off a hanging target, likelyhood is it will be thrown down, or to the side, or somewhere other than straight back. Thus, yes, steel is good to shoot at, but don't put a steel plate on the ground, or braced against something, and ESPECIALLY not facing straight back at you.
Look up on YouTube a video of a gent who's Barrett .50 took his earmuffs off for him at moderate range (150-200yds?). He shot at a steel plate resting on a gravel/sand hill backdrop, it pinged and came straight back.
I will say - for long range shooting, i.e. 800+yds, often a target will be set on the ground, as it is less likely to move, and with that range from the target, a ricochet is more likely to land on the ground rather than in you.