IMAP forwarding show IP address to Google servers? I use K-9 Mail app on my phone, and sync my gmail via IMAP.

My question is: Do google servers see my IP address when checking/sending mail? 

I am pretty sure that if I used the gmail app they would see all my IP address at each sync request. Using a 3rd party app like this, do I avoid that?
No, if you tell K9 to fetch your mail from Google's imap servers, then whenever K9 goes to fetch your mail, it has to contact Google at which point Google will know at which IP they can reach you (to reply to the fetch request).  They may not get to know your "internal IP", tho (e.g. if you're behind a NAT router, they'll see the external IP address of the router, rather than the specific intenral IP address of your Android device).