I use what is essentially Smart Tabs¹ (tabs for indentation, spaces for alignment) in JavaScript, and pure spaces in LiveScript/Coco, which complain when you mix.
This seems silly, to me the only benefit of using tabs is so that users can view it with their own default tab size. In which case space-aligned lines would look out-of-place and probably be hard to read
No, because space alignment only happens within blocks of common indent level. It works, try it.
Do you run into issues when collaborating on code? I imagine that the majority of people (either in favor of pure spaces or tabs) have trouble adapting to using both -- I know I would.
Semantic spacing (indent with tabs and align with spaces) is the standard in Go, enforcrd by gofmt. The compiler doesn't distinguish whitespace, though.