Creating Xen Instance Problems


i have some problems with creating xen instances because ssh is not starting on the instances and the IP of the instance always points to a wrong server.
The problem for me is that we have DNS servers that are not on the cloudmin server (bind is running there but we manage all the domains on another DNS server).

Is there any reason that i can not give the xen instance a FQDN and take care of the DNS setup on my own?
Maybe there is a point which i dont think about it - but i dont understand why every instance needs to be a subdomain of the xen hosts name.

I managed to get around those ‘problems’ by setting up an A record before i installed the xen instance and gave that instance this IP. Creating of the instance and setting up SSH etc is working fine than, yet still i wonder why i cant give a FQDN to an instance.