Is a husband's keeping his wife, who admitted to committing Zina (unlawful sexual intercourse), sodomy, and other relations before her conversion to Islam, and concealing her actions, considered permissible and will he be rewarded for it, or is it deemed Dayouthah (cuckoldry)?

If a woman repents before embracing Islam, then her conversion to Islam nullifies whatever came before it. The husband is not obliged to investigate her past, nor is he required to renew the marriage contract if it met all the conditions. Covering for a Muslim woman is not a form of being a cuckold (dayooth), but rather an act for which one is rewarded.