Although VMware states it is best practice to use 2048bit certificates for servers, nothing is said about the CA certificates. VMware vCenter Appliance 5.5 works fine with 2048bit server certs and 8192bit CA certs. VDP on the other hand does not like 8192bit certs.
As we were in the process of enabling a new CA and testing it first with our VMware environment, we could create a new one with 4096bit.
VMware and ceritificates seem to be a complicated, depressing and never ending story.