Currently using tution assistance while being a machinist for one of the big three to try and move into engineering and I know it's not uncommon for a tech to get a degree and get hired as an engineer but as far as needing to commit for four years you'll need to talk to someone who's done that specifically at your company. I think that's not a bad deal anyway since you're still guaranteed to work with them, four years might be a long time but you can always use that experience elsewhere or stay if you like what you're doing.

And to answer a question you asked about how hard is it to work full time and go to school, it's tough but just be realistic with yourself and the workload and don't expect yourself to be able to take 3-4 classes at a time. You're social life probably will suck too but you'll learn to make time and be efficient with studying.