If you don't want to shell out money for getting temporary access to a physical KVM adapter you could try to use QEMU to boot the server in an virtual environment in OVH's rescue mode instead.
Check it out: https://trick77.com/2015/01/17/how-to-set-up-virtual-kvm-vnc-console-ovh-server/
Probably not relevant for CentOS users since this feature is already built in: http://www.centosx.com/install-centos-remotely-through-vnc/
But may come in handy for Debian and Ubuntu server users.
Note1: Might not work for everyone since the CPU needs to support the VMX extension or because the server needs proprietary drivers (i.e. RAID hw-controller)
Note2: KVM = Kernel-based VM, KVM switch = Keyboard Video Mouse switch/adapter