In a no-lose lottery, lots of people put money in a bank; all of them will get their money back whenever they want. Additionally, the bank takes the proceeds from investing their money and occasionally gives a random person a large bonus sum.
My impression is that those who prohibit gambling in halacha based on problems of asmachta (conditional or implausible obligations) would have no problem with this, you put $100 in the bank and you'll certainly get at least $100 out!
There are those who read the Mishna in Shabbos as a blanket prohibition on all forms of gambling however; at the extreme, R' Ovadya Yosef prohibits buying lottery tickets.
Would those poskim view the no-lose lottery as included in this prohibition?