Basically, vxvlan is a capacity to tunnel a large number of VLANs over a single VLAN.
So you have 1000 VLANs internally on a host. That host communicates with another host, with has those same 1000 VLANs, by tunnelling them over a single VLAN. They also tunnel over a single VLAN to a vxvlan aware firewall.
This capability is built into VMware - there are plenty of easily Googled up guides on how to use vxvlan.
A virtual nexus won't help with what your scenario - a physical one however would be nice 
If for example, servers 1-4 had 1000 customers with 1000 VLANs, servers 5-8 had another 1000, then you would only need 1000 VLANs on the switch connected to servers 1-4 (cluster 1), and 1000 VLANs on the switch connected to servers 5-8 (cluster 2), then you have addressed 2000 VLANs despite only have 1000 per switch. This is all I mean by clustering. You can't build a single cluster with more than ten hosts - and it makes sense to stop at around the number you have use this to help segregate your networks further.