Site received a new 3140 cluster so we pulled the shelves in from the old Filer and presented the CIFS shares on the new cluster. We made no changes to DNS, just created a vif with the IP of the old Filer... just verified a DNS lookup responds with the correct IP of the old Filer (which is now assigned to the vif on one of the new 3140s)...
The times I've seen an IP address work where a hostname doesn't is usually when name resolution is not working. It depends what is doing the name resolution. If it's only DNS then there could be an entry in the local hosts table pointing to the wrong IP address. Can you ping the DNS alias of the filer?
If you are still using WINS and NetBIOS on your clients then you will need to add that alias using the "cifs nbalias" command on the filer. I can't remember if that requires a restart of the cifs service or not. You will also need to enable WINS on the vif.
If that doesn't do it then I don't know. Try a packet trace both with the IP address and with the alias and see what the differences are?