None of the Bitbucket items seem to support ssh keys?
I created an ssh key for my Bitbucket team ( "access key" https://confluence.atlassian.com/bitbucket/use-access-keys-294486051.html) and setup an ssh cred for it in Jenkins.
If I create a new item and specify "Git" as the source I can see my SSH key appear in the "Credentials" drop down.
If I create a new item and specify "Bitbucket" as the source I can only see username and password credentials I have setup (none of my SSH key creds).
This means I can't create a "Bitbucket Team/Project" item because I won't be able to use my ssh key I generated for my Bitbucket team. This is a pretty significant feature of Bitbucket because when you generate an access key eam ssh key its free and provides read only access to all of your team's repos.