Since the number of Uplinks is associated with the number of physical NICs a server can have they would be limited by Networking Maximums for Physical NICs per ESX Host given on page 6:
_max.pdf
Maximums of 32 Physical NICs given on page 6 is consistent with the DVS GUI.
I suppose in theory there could be in a very special case a benefit to defining more Uplinks on a DVS than there are able to be Physical NICs on each host, but I wouldn't expect VMware to have allowed for that in the SDK.
