They have SeaMicro: http://www.seamicro.com/
And given Nvidia has never tried to do anything on the server, it might be that AMD is already ahead of many others.
What's notable about Nvidia's Tesla offerings is that they sit as a separate 1-2U rack on top of the compute box. The space and power costs of operating Nvidia GPGPUs in a datacenter are nontrivial.
If AMD ships a solid ARM product with some good on-die GPGPU components, that might compete with Nvidia, but otherwise the two are in different spaces even within the server world.
[1] http://vr-zone.com/articles/amazon-orders-more-than-10-000-n...