Yes, it is generally considered acceptable for a non-Jewish person to wish a Jewish person "mazel tov" at their marriage. "Mazel tov" is a Hebrew phrase used to express congratulations and good wishes, especially during joyous occasions like weddings. It is a widely known and appreciated expression of goodwill, and many Jewish people would welcome the sentiment from friends, family, or acquaintances, regardless of their cultural or religious background.
However, as with any cultural or religious expression, it's essential to offer such wishes with respect and understanding of the tradition's significance. If you have a close relationship with the person and feel comfortable doing so, you can also consider expressing your congratulations in a way that feels more natural to you. Ultimately, the sincerity and warmth behind your well-wishes are what matter most in such moments of celebration.