I do not know if it would be approved here, but why would one use EMT for burial when PVC will last forever? As far as minium cover, whenever I have any doubt I always go with 24 inches of cover, sort of guaratees no one will dig it up while planting flowers.
I would say Zero-inches if it's for an outdoor pool or hot tub installation. EMT doesn't appear to be allowed underground for pool feeders or branch circuits, although it looks like it can be used on or within buildings for pool related equipment and feeders with no problem. Table 680.10 lists minimum cover depths for "other approved raceways" in these areas though, whatever those might be.