I also think it is provably fair because I won some time with 0.01btc bet and made it into 0.02btc on one lucky roll.
But I won't test my luck with rolling more than 5 times because one of those rolls can wipe your entire balance on the site so fast. As with any other dice site can do to you as well.
With just one roll you really cannot test how provably fair Yobit system is,but i am pretty sure that it will consume your entire balance if you continue for a longer period of time and i am not even sure whether you could verify your rolls,because i have not rolled in that site with bitcoin ,simply because i do not trust how things work in that site but i did try rolling with a alt but i ended up busting everything and i did not care too long about that,when i checked on verifying my rolls and i could not find that,but i am not sure because i was not serious about the whole process.