I'm using poloniex for trade as well as form lend a small amount. And i never had any problem with lending and as above mentioned, poloniex taking collateral from their users so even if the your loan taker has scammed you can still get your money back.
Is this safe? Ask Karpeles.. 
Polo s quite safe, they make a lot of money from their operations and the only real danger would be some form of hacking.
Where can we find the financial report of Poloniex? I trade some coins there, but not sure if it is really safe.