Jeanette,
I think, you have to define two different Approvers list (one for tasks and one for rules) and associate the AD users to the corresponding group.
When user creates new metapedia term, they have to select the 'Metapedia Approver Group' as the approver and the task will be assigned to the members that are part of the group.
Similarly when user creates new rule, they have to pick 'Rule Approver Group' as the approver and the task will be assigned to those members that are part of that group.
If a user part of 'Metapedia Approver Group' logs in, the user can see only metapedia terms. Similarly the rule approver group user will see only rule tasks.
But accidentally if a rule is assigned to metapedia approver group OR if a term is assigned to rule approver group, they will see that in their worklist.
As for as IS concerns, they are all tasks and the approvers group have access to view all the tasks. I don't think there is a security role that allows viewing one type of task but not the other type.
But if you find a way to make this work, please share with the group
Thanks
Sreeram