yes, the mouse and kbd (basic HID) totally worked without any helper app. this was with:
1. stock 4.1.2 rom
2. rooted (not sure if this makes a difference in this case)
3. generic otg cable
4. powered hub
doubt it makes any difference, but for reference it was:
- logitech marble trackball
both worked great at the same time.
and also tested:
- ibm/lenovo trackpoint usb kbd/mouse.
instead of "mouse connected; keyboard connected", it only said "keyboard connected". but the trackpoint mouse still worked fine. (makes sense, the pair actually shows up as only a single HID - 17ef:6009)
without the powered hub, when you plug the cable in, the kernel sees new usb device, but only 1 - the built-in qualcomm ehci root hub, i.e. the phone sees itself. but not the connected device. at least not with any device I tried.
as mentioned, fat32 stick (single partition) worked fine on powered hub too. extfs should be built in, but I have not yet tried a device with single ext partition (again I'm unsure why, without the helper app, stock os did not like my drive - it could be multiple partitions that it doesn't like, or it could be that it did not like the ntfs partition) - I'll try some tests later with: single-partition exfat, single-partition ntfs, and single-partition ext2/3.
(but even if that fails, the helper app is free and as mentioned worked fine to mount all sorts of things. it was a little slow, I wonder if it is doing fsck every time to every partition...)
I don't know if the samsung cable is made of magical wish-granting plastic or has any special electrics inside, or you're right it could be exactly the same as the generic cables. but for 9 bucks, and the fact that samsung don't claim any extra power requirement, I was curious enough to pay to find out. spamazon sez it will arrive 7/24, so I'll report back about it when it comes.
I was also very curious what would happen if I connect my wired xbox360 controller - dmesg showed that the kernel knew exactly what it was lol - MS xbox controller. but doesn't act as a mouse or pointer or anything. basically, the left stick and the d-pad both work as UDLR arrow keys, and that was all.
one last bit of interesting trivia - from what I've read, people say otg wants you to have your device connected to the otg cable, before you plug the micro-b connector into the phone. but, with the hub, I was able to connect otg to the phone (and at this point the phone will say recognized usb connection, even if nothing is connected to the otg cable), then connect and power up the hub, phone saw hub, then add and remove devices from the hub at will, and the phone was 100% cool with all of that.