If switches were to try to distribute GRE flows between two VTEPs that used a GRE encapsulation, all the traffic would be directed to use only one link within these Port Channels.
Not true. GRE encapsulation is not mandated to use the same src/dst addresses for all flows between given two end points.
You do not need to parse deep into packet to enable good load balancing hash across parallel links when you use GRE as an encapsulation technology.
And what is nice about IP encapsulation all GRE src/dst addresses can be naturally aggregated so from IGP point of view they still look like a single prefix.
Regards, R.
