What kind of armour is it considered for use of greaves. For the greaves from that which lies beneath

I believe it is any Light or Medium armour.

Sorry forgot to mention. What kind of armour for use of the greaves would ebon armour be considered

No armor spell or normal would not prevent you from wearing magical grieves.

Doesn't prevent you but the Greaves only function with light (IIRC) armor.

The Greaves of the Scout function with Light or Medium armor. FiM pg 21.
Dralzen is asking if the Armor created by the spell Ebon Armor counts as Light, Medium, Heavy, or none of the above.

Nods head. Kinda a corker...I honestly don't know what the expectation was in designing the spell. Given the values of AR: 4 and bulk 2 I would guess the spell simulates a heavy armor.

But I'm not very confident in that answer. Maybe it's meant to interact will magical greaves? Or the opposite? ...You don't need proficiency in it so maybe it's rules of interaction are "weird."

I will note that 2 Bulk is a lot to eat from your armor. I personally think it's the least useful of the various ebon spells.

the armor possesses AR:4 and Bulk: 2 which makes it equal to Heavy Armor

I'll see about adding a clarification to the current errata