All the real-life examples I've found for 雨夜 only have the reading 'Amaya'.
With regards to Amayo when considering its overall usage, I did find 3 (or perhaps 4*) examples of Amayo on FamilySearch, 2/3 of them being female. When I checked the DouseiDoumei telephone book data, I've only come across about 3 people with the writing 天代. Although I haven't found any Google results for 天代 with the reading Amayo, I feel it is a more likely writing for Amayo than 雨夜.
*One example is transcribed as 'Amaya', though given the overall context, I have a feeling her name is actually 'Amayo' in this case.
My PNL:
http://www.behindthename.com/pnl/149249'Maybe It Is Daijiro (aka Maks)' blog:
https://maybeitisdaijirou.wordpress.com/'Beyond Sakura and Hiroshi' blog:
https://beyondsakuraandhiroshi.wordpress.com/My Twitter: @maybeitsdaijiro