Yes you can! Yahoo doesn't publicize that they have IMAP settings but they do! Because they have IMAP, we can map in your yahoo mail to Nimble.
1) Go to your Settings in Nimble
2) Click on the Networks tab on the left
3) Click on Add an IMAP Account
4) Type in your Yahoo email in the Email field. The username field will automatically populate.
5) Enter your password. Check off Use Secure Connection
6) For the IMAP Host field, type in: imap.mail.yahoo.com
7) For the SMTP Host field, type in: smtp.mail.yahoo.com
8) IMAP Port: 993 with SSL, SMTP Port: 465 with SSL.
9) Once validated, Nimble will ask you to map in your folders from Yahoo