It does work with the Resource Manager...
The "Source" custom field you have created, was it just a single line text box or was it a rich text box?
The auto linking which is the opportunity I use to grab the URL, and find its title, is very much a "rich text" (bb code) operation. For it to work it would have to be a rich text box.
There would be no way to make it work with a single line text box.