There can be a lot of dangerous signs around money, and your mileage may vary on when it's okay or not. Prior to leaving I was OK, if wary, with 'Em so X can't make rent this month, is it OK if we take 500 euro from your salary so he can use it to pay rent? We'll get it back to you.' Of course that really meant 'We are not going to pay you as much any more, good luck getting it back'.
Funny you say that, these startups actually wanted me to be referred to as a cofounder even though I wasn't. They actually leveraged that title to make me sacrifice salary and work much harder than I should have (i.e. many all-nighters). When I found out funding was running out and I was only being paid enough to cover rent I had to leave.
*Worked for two startups that couldn't make payroll. CEOs promised money was around the corner so I kept working. The money never came.