Network Address of Subscriber Objects

When I look at a Distribution in Imanager's Tiered Distribution View,
Some of my Subscribers show up with the IP address.
I have gone into the Object in NDS and checked under the Other tab and
looked at the Network address. On some Subscribers I have a TYPE_13 that
has the DNS and some that have the IP in the TYPE_13. On other
Subscribers I have both a TYPE_13 field and an IP field.
My question is
1. Is there any issue with changing the TYPE_13 field that has the IP
address to the DNS name as it should be.
2. Is there any issue with leaving the extra field IP in place.
3. does adding the field IP to my subscribers get me anything ?