Rain is only a negative for underwater photographers as it usually means clouds and darker skies. My favorite positive about the rain is a nice fresh-water shower to rinse my face and hair after ascent while waiting for the boat pickup.
Occasionally it can turn into a bit of a squall, but there's no difference underwater. It just makes the boat rides more interesting. That said, should you happen to ascend in such a condition where surface visibility is poor due to a hard rain, be extra alert for boats and ready to quickly re-descend if necessary, wave your sausage extra high, or best yet, stick with the DM/group and don't get separated in the first place.
Occasionally it can turn into a bit of a squall, but there's no difference underwater. It just makes the boat rides more interesting. That said, should you happen to ascend in such a condition where surface visibility is poor due to a hard rain, be extra alert for boats and ready to quickly re-descend if necessary, wave your sausage extra high, or best yet, stick with the DM/group and don't get separated in the first place.