Nope -- anybody can get the free 200 MB. ... If you're on the fence, I'd say go for it and grab a T-Mo one.
Correct, I've got two tablets on the 200 plan, no tmobile account in my name. Except the two free 200's

. One tablet is an ATT ipad 3, and the other is a verizon ipad air.
I would suggest not getting the tmobile air or rmini. Go for the Verizon ( or sprint if you must). The reason is flexibility. Both sprint and verizon lock their networks to only work with iPads sold for their network. The iPads are technically unlocked, but sprint and verizon record the serial numbers of those sold with their sim, and only allow those iPads on their network. Technically the ipad is unlocked, but the carrier network is locked.
You can use a verizon ipad air/rmini on the verizon, tmobile, and ATT networks, all you need is the correct network sim. The same is true for sprint except obviously it is limited to sprint, tmobile and ATT.
If you get a tmobile or ATT ipad air/Rimini then it will only work with tmobile and ATT. Some folks have reported that they can get a non-verizon ipad to work with a previously activated verizon sim, or by getting a customer service rep to enter the iPad's serial number into the verizon database, but this is not guaranteed. I've not seen posts by anyone who has gotten sprint to add their non-sprint ipad to their network.
In short, why limit yourself, get a verizon ipad air one rMini for maximum flexibility at the same price.