Shade
Monster Junkie
Well I think following the summon nature's ally progression makes more sence, I'm willing to humour your continuum fetish if it'll make you happy.
The question is do we want to close the gap down or up?
Close it up. I think the monolith should be at least 9th-level.
When a healing spell forms a Living Ash out of the ashen wastes, is the creature only temporary (emerging for a few rounds and then disintegrating back into the wastes) or is it a permanent creature?
That's an excellent question! Unfortunately, I have no answer.

If it's temporary like a summoning spell I'd be happier with a lower level version.
If it's up to us, I'd go that route.
Also, I'm wondering whether the entire Ashen Wastes is one really big Living Ash, and the healing spells only "wake up" comparatively tiny portions of it. Maybe they're antibodies released to destroy destructive Positive Energy infections?
I'm terribly unfamiliar with the Dragonlance source material from whence this came, but that's a great idea for genericizing it!