Yoga - even just for alignment - can be bad news. There's no guarantees, and there are a lot of people who have wound up injured and even disfigured from doing yoga. I'm not telling people not do yoga if they seriously want to study, but I would say be careful. And it's certainly not worth it, or necessary - to approach it for basic alignment. And there again, we'd be sending people into services that overhaul cars, when what they really needed was just a quick in-and-out Jiffy Lube alignment.
That's a very broad=brush dismissal of yoga, if you don't mind me saying so.
In even my somewhat limited experience of the wider world of yoga, there is at least as much of a range of focus and competence as in aikido. I have practised with several yoga teachers, and, while I believe that the way I have been studying for the last five or six years is extremely congruent with where I am trying to take my aikido, there are some yoga traditions which take the body structure in completely the opposite direction. And that's only the (excellent) teachers that I have come across.
I would strongly recommend finding a yoga teacher with a direct and verifiable line of descent from Vanda Scaravelli. This way of training really emphasises postural strength and developing awareness of the spinal (particularly the psoas) and pelvic muscle groups, which has revolutionised my approach to posture.