Validating HTTPS clients with certificates signed by other CAs than server's CA
Found out what's the problem. The certificate is signed by a chain of 3 CAs and I set SSLVerifyDepth to 1. Set it to 10 and it worked.
I believe you want a directory containing the certs you want to use. You may need to use some SSL magic to create the symlinks for the certificates. See mod_ssl SSLCACertificatePath Proper Usage or What is the Best way to Handle Multiple Acceptable Client Certificate CAs for the required commands.