Allowed? Yes. Bids by the auctioneer? No. By a third party with the the proxy user disclosing bidding terms with the auctioneer, garnering permission to proxy? Yes, mandatory. Proof of Proxy? PoP, which would be the discussion between the three parties involved MUST be publicly disclosed after auction ends.
Alternatively ... Just have a friend bid it for themselves... Escrow the funds prior or give the funds to said friend directly.
These are the cleanest ways to ensure no fuckery imo.
I would be content with these rules