Yes, there are. For example, in some novels, Aphrodite, the goddess of love in Greek mythology, might be featured in a romantic plot. Her beauty and power over love can add a lot of interesting elements to a love story.
Definitely. Greek gods have such rich personalities and backstories that they are perfect for incorporating into romance novels. Poseidon could be in a story where a mortal falls in love with him, and they have to overcome the differences between the human and divine worlds for their love.