Yes, you can tie all the grounds you mention together. In general though, you don't want to do a star ground. Star grounds work best when you have high currents and low frequencies. Microprocessor systems don't fit this description. You should be using a single full ground plane with all grounds routed as directly as possible to the plane.
I have a MC52233 based design where I use the AtoD converter and I've tied VDDA and VRH directly to the 3.3V supply. I do have a pretty clean 3.3V though as I'm using a linear regulator from 5.0V down to 3.3 to run the Coldfire. I don't think there is a universal correct answer on the analog supply. If you have lots of digital stuff on the 3.3V or you use a switching supply you may want to put a series ferrite bead and some bulk decoupling on these pins. It also depends on what you do with the AtoD. I'm monitoring some low frequency process stuff, so I do averaging in software to remove noise. If you are converting wider band signals such as audio, you can't apply this approach and you need to be more careful here.
Hope that helps.
