It is similar to collateral for your margin tradings. It should be in stable coins (a strong one that should be old enough. I don't trust new stable coins). If you use Bitcoin especially altcoins as collateral, you will be more easily liquidated.
I don't think one trading inverse contracts gives them a more likelihood of their position getting liquidated as compared to a position of a linear contract. It has more to do with the rise and fall in the value of the underlying crypto asset, which translates to more or less profits in USD quoted from the base currency.
Using people's money as collateral even with stablecoins can still fuck things up if the market goes against the opened positions. Stablecoins do make the positions bulletproof from liquidation. The problem is too much greed by the so-called exchanges.