>Does Shimano recommend tandem use or spec weight limits? <
Shimano dosen't even recommend the use of a 3 speed grank up front with the Nexus so probably not.
Weight limits? Well the long recumbent I took it off is twice the weight of the tandem and I've used it without problems on that the last 3 years.
Nexus seems like it's imposable to kill to me but I'll keep trying
