Which casinos do you mean, in particular? I am not sure about sharing the results, stats or even the jackpots between non-partner casinos. However, many casions belong under one provider (e.g. Spinamba, FortuneClock and some others, all operated by one company...) - but this is just my non-professional opinion.
However, what I am pretty sure about is that many slot providers/developers offers their solutions to end-customers (casinos) and I could imagine that within the service package there might be some option allowing cross-sharing certain data. For example if I start my own casino right now, I would appreciate if my slots would be conneted in some kind of network with shared pot, because it will help to attract new customers. Here's an example of what I am talking about: https://www.softgamings.com/ maybe you found the answer out there......