Install existing SSL certificate on Dell iDRAC7
After giving up a few times I finally figured out how to upload an SSL certificate with the RACADM command:
racadm -r <ip of idrac> -u <username> -p <password> sslkeyupload -t 1 -f filename.key
racadm -r <ip of idrac> -u <username> -p <password> sslcertupload -t 1 -f filename.cer
After running the second command, the server rebooted, iDRAC web interface was down for a minute, but when it came back, it was using my custom SSL certificate.
This page should tell you how to obtain RACADM if you don't already have it.
If you run it (as an administrator account) on the server you are trying to modify, you can leave off the -r and IP parameters. This is important if you are using iDRAC Express which does not allow remote RACADM access.
NOTE: If you've changed the HTTPS port of your iDRAC interface, you will need to specify :, As RACADM appears to use the HTTPS port for remote access.