Yes, I've imported PADS gerbers into Allegro. Wasn't easy, but Cadence can help.
What I had to do was generate a "PADS-like" art.param and aperture.txt file; then experiment with the Allegro UNITS until I could get it to come in. Once I knew what the setting needed to be it was pretty easy.
One note, you'll need to work with the aperture file until you get the "dimensionals" correct. It took some time until I could get the unit variable right (2,3 or 3,4 or 3,5, etc.)