The Icelandic summer has been rather wet. Rain won't be considered photographers' friend anytime soon but there’s no reason to stop trying. Personally, I think some of my best images are taken on cloudy days that are threatened with rain.
The cool thing about Iceland is that so often you can find dry spots on rainy days that will provide you with excellent photo opportunities.
This is one of the key reasons why you should consider hiring a professional photo guide. You are hiring a local that knows the locations and the weather in Iceland and is, therefore, more likely to present you with good opportunities.
I recently took a lovely couple from Australia on a three-day tour which unfortunately didn’t see much sun at all. But nonetheless, we were able to catch some nice images along the way.