the wordpress plugin terms state that
The plugin must not embed external links on the public site (like a "powered by" link) without explicitly asking the user's permission.
If the plugin acts as an interfaces to some external third party service, may the external third party service display a link when embedded to the blog by the plugin?
Example: The disqus comment system has a DISQUS logo with a link to the disqus homepage. Is this acceptable or not?