Why is SubmitDiagInfo failing on Yosemite?
When your Mac generates diagnostic logs, submitting them to Apple helps them know what issues are actually happening as opposed to one person reporting a bug. In the long term, not sending any reports is bad for you since your issues will be underweighted / undervalued and other people's crashes will possibly get more attention.

In the short term, one or two errors likely won't make any difference.

To figure out the error, you could use the command line to open a test connection to the server indicated in the failure message:

openssl s_client -connect radarsubmissions.apple.com:443


Several lines of text should flow by if you have no errors or issues. The tail end of a successful test should look like:

SSL handshake has read 2962 bytes and written 456 bytes
---
New, TLSv1/SSLv3, Cipher is AES128-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : AES128-SHA
    Session-ID: 9B9A3A1B0136419E428B0857BEBDE5CA2EC2276083B9A6568943E475B59D7F25
    Session-ID-ctx: 
    Master-Key: 976B51D8E678BB520EEB66BB701510F40620551AFE88A51D62F0167434D9695A0784A4DDA8956CE1EBA73ED034BA8AC5
    Key-Arg   : None
    Start Time: 1445003611
    Timeout   : 300 (sec)
    Verify return code: 0 (ok)
---


At this point, you wan wait for the timeout or press control-D one time to exit the openssl test connection. The obvious thing that would break is if your computer and Apple's servers thought the time now was more than 4 or 5 minutes apart. You can go to your system preferences and toggle the "set time automatically" switch once or twice to get your clock updated with Apple's public time servers.