Glad you got it figured out. If you hadn't already seen the Wiki, I was going to point you in that direction. It appears you already found it.
It's just personal opinion, but it's generally best to install DLG on a clean Slackware system (e.g. without a previous FRG install) and vice-versa. However, if everything seems to be working okay, then I guess there are no worries.
We'd love to include NetworkManager with the 2.14.0 release of Dropline GNOME. It's a great tool. Unfortunately, there are some problems in Slackware's dhclient, but suggestions have been sent to Slackware.com to improve this. Additionally, I believe that there need to be some added dbus bindings (which are missing from Slackware's package) in order to make things work.
For anyone else who is interested in making NetworkManager work on DLG, FRG, Gware, etc. - please see this wiki.