Does Cloze support iCloud, Yahoo, and other IMAP aliases?

Yes!

Cloze lets you send messages with another of your email addresses listed as the sender instead of your iCloud, Yahoo, or other IMAP address.  

1.) Tap on More (...) in the lower right of your screen on mobile (iOS/Android) and lower left on cloze.com.

2.) Tap on Settings

3.) Tap on Connected Accounts to expand the section. Then click on the settings (gear) next to email address to which you are adding the alias.

4.) Enter your Email Alias and tap on the OK button.

5.) Once added, you can then select your email alias account in the email composer.