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.
To be honest, you as lender have no collateral if control over collateral have someone else - here Poloniex.
Is this safe? Ask Karpeles..
Well before you be able to get a loan you need to use the margin trade and put some coin into there,then when you get a loan you will know the interest you will have to pay ,and its a low fee,you cant withdraw the money out from poloniex soo you must invest it there soo i believe lending there is safe ,atleast your bitcoins will stay at the exchange and for my own experience i got paid for all lends i had there soo i cant complaint,the fee is very small and lower then here.