Hmm, lets see:
Support for G4 PowerMacs and eMac announced for MorphOS2.5.
Videos uploaded showing an expermental branch working on Powerbook.
The guys listed in MorphOS->about allmost constantly online in #morphos
See no reason why it shouldn't still being developed
Short answer: Yes, it is in active development.
MorphOS is great. Very fast, very stable, very compatible, excellent native programs (ShowGirls, OWB, MPlayer, etc.).