I made the experience that it is possible to connect to the Task Service of a client which has firewall on and "Allow Remote Task..." deactivated.
It is very simple. I created the following code to be able to handle XP machines I couldnt connect the "normal way". Always getting "...not supported". Then by "accident" I started this code against a 2008SP2 Client with firewall
on and "Allow Remote Task..." deactivated:
ts = new TaskService();
ts.TargetServer = <ip addres of machine>.
After filling up the ip address it gets connected to the machine. Well it looks like it doesnt fully support everything. Sometimes tasks are schduled and dont run automatically. But I am able to define tasks, monitoring them and start them when they need a
little bit extra help.
Hope this helps someone running into the firewall problem.