Yes, Fiddler can grab the certificate information, but today that's only
if you have enabled HTTPS decryption. You're correct that Fiddler returns its own certificate to the client in that configuration, but that also means that Fiddler must itself verify the server's certificate to ensure that it is free of errors before it returns its own (error-free) certificate to the client.
You can see the information that Fiddler itself keeps by selecting the CONNECT "Tunnel to" entry in Fiddler's Web Sessions list. Click the TextView response inspector and you'll see text like:
Encrypted HTTPS traffic flows through this CONNECT tunnel. HTTPS Decryption is enabled in Fiddler, so decrypted sessions running in this tunnel will be shown in the Web Sessions list.
Secure Protocol: Tls
Cipher: Rc4 128bits
Hash Algorithm: Md5 128bits
Key Exchange: RsaKeyX 2048bits
== Server Certificate ==========
CN=www.bayden.com, OU=Domain Control Validated
CN=Go Daddy Secure Certificate Authority - G2, OU=http://certs.godaddy.com/repository/, O="GoDaddy.com, Inc.", L=Scottsdale, S=Arizona, C=US
11/8/2014 7:22:06 AM
4/10/2018 2:36:48 PM
Now, if you want to get more elaborate information out of the certificate, you can do so by examining the certificate from FiddlerScript while the connection is active; see the Adding Custom Information section of this blog post: http://blogs.telerik.com/fiddler/posts/14-09-30/visualizing-security-information-with-fiddler
All the best,