Hiring for culture is crucial, technical skills can be augmented as long as the aptitude exists.
I have been on several growing teams and keeping the culture the same as you grow is difficult. Those who were there since the beginning tend to be the ones who miss "what it used to be like." They see the dynamics change as more people are added. This is a hard one to stay on top of, but it MUST come from the top down and management needs to stay engaged.