Yes the Galaxy S4 Active (all variants) use Knox for the kernel protection as I understand it. Can't speak of the SIM region locks at this time as I've got the AT&T US model (I537) and I have no intentions of going international anytime soon (read: ever). I unlocked mine for use with T-Mobile and haven't had any issues so far myself.
If you do most anything to the Active Samsung has ways of detecting it. I just got home from trying to have a Samsung rep at Best Buy restore mine to the most current official ROM build for the I537 (which is MF3) and because either a) mine has been rooted in the past but isn't rooted at this moment or b) because mine is carrier unlocked or c) a combination of both a and b I'm unable to get it flashed back to MF3 which was the OTA update to MF2 (what this phone had on it when I got it). The Samsung flashing software could see my device and detected the specific ROM build but called it "not compatible" and refused to do the MF3 flash so that's that.
There's not nearly as much info or development for the GS4A as the GS4, but what info there is you'll find here in this subforum just for the GS4A.
It's a great device, but the locked bootloader is cramping it and keeping it from really taking off, and it's waning popularity in stores and low sales are definitely something that the carriers are taking note of (especially AT&T who may stop selling it before the end of the year from what I've read rumors of).
As for a Samsung "guide" for iPhone users, well, it's basically Android even with Touchwiz (Samsung's craptastic UI they force on their device owners) so any old guide for Android should prove useful. The GS4A user guide is a good place to start.
If you want something a lot more comprehensive there's a magazine on the newsstands right now that I would recommend if you want "hard copy" to work with:
Just came out (that is a picture of Volume 2 - Volume 1 came out in late 2012 and has a different cover so make sure you get the right one as pictured above) like a month ago so it's pretty much as up-to-date as anything else can be. Runs about $15-20 at most bookstores or online, and there's a PDF version available as an eBook too from Amazon iirc.
Hope this helps...
Currently in between devices...