I still think the server graphic card is not the main reason here, since it used to work with the KVM earlier. Do check on these discussions
http://www.techsupportforum.com/forums/f25/solved-kvm-switch-issue-268221.html
http://en.community.dell.com/support-forums/peripherals/f/3529/p/18801340/18929887.aspx#18929887
Accessing the KVM console will not disturb your production environment. I am will check on any resolution/refresh rates available for ESXi server from command lines or using boot options.
Thanks,
zXi