So it seems after a little more digging you can actually fix this. However looks like you need to do so from Apple Remote Desktop, as that's the only place from where you can tell "remote management" to allow users from your Open Directory domain.
Easiest way seems to be first to add some new groups using Workgroup Manager, there are four specific names you must use for these groups, ard_admin, ard_interact, ard_manage, and arp_reports, each giving various levels of access. Create the groups and add the relevant people into the relevant groups. The ard_interact groups seems to be the one to use to manage screen sharing. The second step is then using apple remote desktop you need to select the clients you want to update and choose "change client settings" from the manage menu. There is then an option on the third screen called "enable directory based administration", selecting this will allow those groups access to remote management with the relevant privileges that come with each group.
Note even after you have done this, you will not see any difference when you look at the remote management system preference, but it certainly worked for me.
More details can be found in the Apple remote desktop manual round about page 69, 79 in the section titled "Apple Remote Desktop Administration using Directory Services"
Hope this is useful
Dave