Can I use pre-regulated PoE power safely/within specifications?
The problem is that POE isn’t unregulated anywhere.

As to the safety factor, that probably moot, because a standard Poe supply is going to shut the powered device down if it pulls too much current. Also, who is going to want to buy or use something that isn’t Poe compliant?

As to the physical aspect of it, it isn’t realistic to do this. 30w/48v is 0.625a. While I don’t know your application exactly, I believe this would take a carefully crafted power supply and motor control to work around the limitations.

You might check out some of the Poe options from LT/analog devices for greater than 30w options.