From the GNS530 Manual:
"The GNS 530 allows the pilot to fly non-precision and
precision approaches to airports with published instrument
approach procedures."
It goes on to say that all such approaches are stored on a Jeppesen data card. So if the approach you want to use isn't in the Jeppesen database, the GNS530 can't be used to legally fly it.
Not an Agusta restriction, a Regulatory restriction. When the 109S came out (2005) I guess WAAS was still in the future.