Is it possible for an admin to accept skills endorsements or add skills on behalf of other users? Alternatively, is it possible to turn off the need for users to approve their endorsements? It seems like this should be an Admin Console setting under "People", but I can't find one.
Reviewing through your request, while it is possible to disable this feature completely via your admin console >> people >> settings >> global profile settings page:
The ability to disable the approval process is not available in the current product. As such, I would suggest submitting an idea to the Ideas for Jive space, if this is a feature you are interested in.