I don't see why uncle rewards cant just be distributed in the same manner as normal rewards.
Ethpool came about when people grew tired of the overly complicated and obscure payout lottery implemented by the parent pool ethermine.org.
It was pretty clear to me from the start that any admin using this system is not someone I would trust with any major hash power.
If they distributed uncle blocks exactly as they do with "normal blocks" they could not steal without being easily noticed, using this other reward method, they may claim that their wallets addresses are luckier than the pool users, so they can get all the uncle blocks for them (1030 ETH +- stolen in the last month).