Yes, you can do your OpenGL programming on Ubuntu. OpenGL 2 is effectively a superset of OpenGL ES 2, so if you stay within the confines of the ES features, you'll be fine. Mesa also supports the ES2 profile, so you could have a look at that. But if you want to write for mobile devices, having access to one will serve you well.
I'm sure other people, and Google, will can link any number of tutorials; I remember this book as being helpful http://www.amazon.co.uk/OpenGL-ES-2-0-Programming-Guide/dp/0321502795
Do you mean if there's a chance to learn the fundamentals in 6 months? Yes, definitely! Especially since you probably already know a lot of the basic concepts and math from XNA.
Making an indie game can pay for college roughly the same way buying a lottery ticket can, unfortunately. It's possible, but luck plays a huge factor.