I have two meteor applications connected via DDP on different servers and server A send data to server B. This is the way they work.
Server A
I think you are not passing DDP connection object to the Collection correctly, try:
var remote = DDP.connect('http://server-a/');
Items = new Meteor.Collection('items', { connection: remote });
It might be useful for debugging to try all these connection games from the browser console first, since Meteor provides the same API of connection/collections on the client (except for the control flow). Just open any Meteor application and try this lines from the console.