Yes, it is absolutely okay to propose with a non-diamond engagement ring. The choice of engagement ring should reflect the preferences and values of both the giver and the recipient. Non-diamond engagement rings, which can feature a variety of gemstones such as moissanite or cubic zirconia offer unique beauty and symbolism.
Many couples today are opting for non-traditional engagement rings for various reasons including personal style, budget considerations, ethical concerns regarding diamond sourcing, or simply to express individuality. What matters most is the sentiment and commitment behind the proposal, rather than the specific type of gemstone or material used in the ring.