I think loaning Bitcoins is a great way to gain some Bitcoin while holding your investment. If you can find the right exchanges that allows lending, it can be safe as well.
It still involves risk either way even if you find the right exchanges that allows lending. I agree with you that sometimes it can be safe since it will only involves a little risk. I would recommend everyone who wants to lend their bitcoins to traders poloniex.com just like what OP said since it is a good and known exchange and it is safer doing it there. Crypto-games.net is good too for those who want to invest on bankrolls for casino.