Depends; the marital union is unique (in law and practice), and you haven't said whether the other hypotheticals I posited (de facto large equity position, industry expertise, or a tradition of being effectively helpful) may also exist.
Mixing business with family is always fraught with danger. But it works for a lot of startups.
It's often better to formalize roles & titles, to help everyone reach similar knowledge about real power/responsibility – rather than relying on tacit knowledge, which varies with tenure, social skills, and (in the extreme) romantic relationships. But lots of startups have done well with, and even earned praise and fame for, their low-formalities, low-titles, low-hierarchy, environment.
Mixing business with family is always fraught with danger. But it works for a lot of startups.
It's often better to formalize roles & titles, to help everyone reach similar knowledge about real power/responsibility – rather than relying on tacit knowledge, which varies with tenure, social skills, and (in the extreme) romantic relationships. But lots of startups have done well with, and even earned praise and fame for, their low-formalities, low-titles, low-hierarchy, environment.