default login for Dell networker vproxy appliance

URL? I think you might have the wrong idea of how to use and manage a vproxy? It has no web based interface. You add it to the NW server via NMC or NWUI (the latter if NW version used is high enough).

The vproxy password might depend on the platform where you have deployed the vproxy on, as for example the nw19.5 manual states about VCenter deployment:

"NOTE: The passwords for the root and admin account should be between 8 and 20 characters in length. Specifying a new password is mandatory when deploying the vProxy using vCenter, otherwise the vProxy appliance fails to power on. Ensure that you change the default passwords of both the root and admin account during deployment."

So that applies also to VC deployments on Azure or AWS.

So if it is another kind of deployment, without you or someone else setting root and admin passwords during OVA deployment in for example vmware workstation, they would be the following:

NOTE:
● If you are deploying vProxy on an ESXi 6.0 directly using vSphere client then you do not have an option to set the vProxy password during deployment. You must change the default passwords from the console window of the vProxy appliance or use the default passwords to configure vProxy once deployed . The default password for root account is “changeme” and for admin account is “a3dp@m8n”.