To me, this issue becomes a Brisker question. Is zdakah a din in the gavra or in the chefttza? If the mitzva is on the gavra then fine, I give my donation! If the mossad or the meshulach are crooked or are con men, that’s on their heads. If, on the other hand, the cheftza of zedaka is the mitzva, then I, as an apitropos of Hegdesh, must take due diligence to assure that the donation is to a person or organization that is on the up and up.
I agree with APY that is is extremely distasteful and disrespectful to feature Gedolei Yisroel as shills for this or that organization.
Note to Milhouse: Some citations would lend verisimilitude to your blanket statement.