Is the Velbon df 50 tripod for the Nikon d3000 compatible?

Is the Velbon df 50 tripod for the Nikon d3000 compatible?

Yes. The tripod mount on DSLR's is actually one thing that had been standardized.

Just about ANY tripod is compatible with ANY camera with a standard tripod bush - so, yes.

You asked if the tripod is compatible and answers received (so far) reference to the tripod screw of 1/4" by 20 thread.
I'm not familiar with the tripod you want. But I mount my camera on a tripod and see how steady it is. I then remove the camera and press with the heel of my hand on the top of the tripod and see how much the tripod "dances" on the tile floor. The least dancing gets my vote!