This is taken from the Diccionario de Terminología Jurídica Mexicana de Becerra.

Visitador - inspector, auditor, overseer, overlooker, regulator, examiner (usually from the government). Visitador judicial - court inspector, judicial inspector. Visitaduría - inspection office, office and function of a government auditor or court inspector. Visitaduria judicial - court inspection office, judicial inspection office.

Actuario - actuary, court clerk, court officer, sheriff, deputy sheriff, marshal, officer of the court in charge of delivering service of process, court summons and other personal notices, and also who is in charge of evicting tenants, attaching property, executing judgments and implementing other court orders outside the court house, the correct term SECRETARIO ACTUARIO; there is no exact equivalent in the U.S. system, though some of this officer's functions may be similar to those of a sheriff or deputy sheriff: el actuario debe llevar un libro en el que asiente diariamente las diligencias y notificaciones que lleve a cabo fuera de la oficina del juzgado/the court clerk must keep daily records of all actions taken and all notices that he or she serves outside the court house.

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Note added at 18 mins (2005-11-28 14:52:38 GMT)
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Your question was "do they have similar roles". It seems that the visitador (if he is a visitador judicial) does court inspections. The actuario delivers summons, is in charge of evictions, property attachments and implementing court orders. As Becerra indicated, there is no exact equivalent in the U.S. and his suggested adaptation is "court clerk".