> What is the actual state of this DE? Is it used by MorphOS and
> still beeing under developement?

The MorphOS 3.11 ISO image contains the Ambient changelog, so you can have a look yourself.

> Is it possible to dualboot without osx CD [...] and is there any good guide for this?

Yes, you can add a MorphOS installation to an existing MacOSX installation. This guide has everything needed.