Conceivably, but the Donkey-blockchain must have been created with a higher-than-50% limit on what an attacker would need to steal.
It's a tradeoff against censorship risk: So, in one example, the attacker might need 90% to steal, but then he only needs 10% to censor return transactions.
Thanks for the replies. I guess I was thinking that for a blockchain to be part of the sidechain experiment, it would probably be helpful to have many active users and hopefully not be dominated by large mining ventures?