Here is what happens when Raziel shifts from the Material Realm to the Spectral Realm:

Raziel stands in the middle of a circular stone platform in a grass clearing. There are six, straight stone pillars ringing the edges of the platform. Raziel shifts into Spectral, and suddenly everything around him warps and distorts. Everything around him is suddenly tainted a weird greenish/blue glow and the stone pillars are no longer standing straight, but are crooked and curved now instead. This once open grass clearing is now inhabited by a number of free-floating souls, and a few soul-scavenger creatures named Sluagh. Raziel devours a few souls, and is back at full health in no time. He sees a shift point located in the grass about 15 feet away from the center of that stone platform. He steps into the shift point, gathers all of his spectral energy and manifests himself in the Material Realm. From Raziel's perspective, it feels like about 15 or 20 minutes have passed since he shifted into Spectral.

This is how it would look to anyone who was watching Raziel shift:

Joe is standing about 30 feet away from the stone platform. He sees Raziel suddenly dissolve into nothing. The very instant that Raziel dissolves in the center of the platform, he re-appears 15 feet away from the platform, good as new. To Joe, it would appear as though Raziel teleported and healed his wounds at the same time.

So, no Raziel could not just shift back into Material behind Kuja and attack him, unless Kuja was being stupid enough to stand right in front of a shift point the instant Raziel shifted. Plus, Raziel can't see creatures that are in the Material Realm if he's in the Spectral Realm. He would just have to remember where Kuja was when he shifted.