What would someone's unofficial support of another be called? [closed]
Solution 1:
Unwitting beneficiary, unwitting conspirator, unwitting partner.
Unwitting (definition 2)
not knowing; unaware; ignorant; oblivious; unconscious:
Solution 2:
In your scenario, answering the question posed in the title, I think Putin could be called the silent benefactor, anonymous donor or secret admirer.
Perhaps we could call Trump the unknowing beneficiary or natural ally.