Number of tickets can be easily rigged so it means his idea is not good because final result can be rigged as well.
If you want true provably fair lottery than post here sha256 hash server seed for next week, and on Sunday announce - lottery is closed, total number of tickets sold is "n", then find member with highly green trust and let him post random "client seed" for that week.
After you do all that, reveal server seed, use your multiplier game(modify it with number of tickets), add nonce up to 10 and than roll number 10 times.
All 10 numbers rolled in a row will be numbers of winning tickets.
Make it public!
I don't see what is more provably fair than this and we all can verify it!
I know this sounds very complicated, but if you think about it you will see it's not complicated at all and it will prove your lottery is provably fair!
Your post intrigues me, but I do not understand the final part of the drawing. What do you mean by 10 numbers rolled in a row? Do you mean they are added together?