So is this more grammatically accurate than to say 'wamerekani wanaishi marekani' or is there a specific context in which one or the other is more appropriate?
I believe that wanaishi is the present definite/continuous, whereas huishi is the habitual. It would be the difference between;
Wamarekani huishi marekani. Americans live in America,
and,
Wamarekani wanaishi marekani. The Americans are living in America.