Two connections into an ensemble

If there is an ensemble and two different nodes are connected so that both of the nodes are inputs to the ensemble. (ie. when there is an ensemble ens1 and two nodes, node1 and node 2, Nengo.Connection(node1, ens) and Nengo.Connection(node2, ens) ), how do these inputs contribute to the ensemble?
Does the ensemble take the summation of the outputs from the nodes as an input?

Yes. Although subject to the parameters in nengo.Connection(), e.g. if the outputs of the node1 and node2 are spikes and you are using your above code to connect them to ens1, then the output spikes would be synapsed by the default value 0.005 before being summed up in the input to the ens1. Of course, you may also be required to account for the transform and/or function parameter, etc.