ArmA 3 yes. ArmA 3 Milsim/relaxed realism? No.
Most viewers we have in our current streams are the result of advertisement and in that case the platform doesnt really matter if it is easy to use and nice to watch. The first streams we did were on Twitch by the way. Reason was that Youtube Gaming wasnt avaible in germany at the time for me. I can tell you that in the last 4-6 weeks we had more "unrelated" viewers on youtube gaming as on twitch. The main reason is that the competition is smaller and when we are streaming we are on the front page when it comes to anything thats related to ArmA.
Comparisons to ArmA Finnland also dont work because ArmA Finnland is pretty much Finnland playing ArmA with the exeption of Whiplash and Arf.
A few years ago I did livestreaming on a relatively popular streaming channel that usually had 200-400 viewers at the time for most streams that were going on and I think I have some experience in that matter. I can tell you that especially the crowd on twitch has little to no interest watching normal sunday operations or ArmA 3 milsim in general. There is too little going on for them on the screen and so the majority of the viewers are somewhat related because you did advertisement on ArmA 3 forums, Twitter etc. The midweek operations are relatively good to stream because they are shorter in lenght and they are usually also very compact when it comes to gameplay. You will rarely watch somebody walking in the woods for 30 minutes without anything going to happen. That is a reason why I would personally not stream usual sunday operations with the exeption of special events like this sunday.
From the technical perspective Youtube Gaming is right now also a better platform. Especially during peak times twitch can get "hickups" especially when you are not a "premium user" there. Beside that we have that content all in one channel and the same goes for subscriptions, comments etc. Another good thing is that very often the viewers there have their own channels and so you also have a community & social media aspect there.
Beside that streaming is a nice "gimmick" but nothing thats too important. If people want to become the next big thing on twitch, hitbox or youtube gaming, they should do it somewhere else and my advice is to play a different game or game mode.

Beside that this thread is not meant for discussions about what, how and where members of the 3CB decide to livestream content.