It would appear that Vine Server 3 and 3b2 do not let viewers request exclusive access (when that option is selected in Vine Server)
Steps to Reproduce:
In the Preferences for Vine Server, select “Let viewers request exclusive access”.
Start Vine Server
Start your Viewer of choice (and make sure you enable “exclusive access” or NO sharing in your viewer’s preferences). e.g. By default that is the case with Chicken with the Sea. With other viewers you will likely need to specify that the viewer has exclusive access. eg. with the Java Tight VNC viewer, specify ‘“share desktop” no’ on the command line.
Connect to Vine Server
Run a second viewer and try to connect to your vine server.
You can! Both viewers are connected.
It appears that Vine Server (3.0 or 3b2) is not letting Viewers request exclusive access.