I had trouble getting the EI segments to be found by the UA agent and added into my itinerary. She checked with her customer service and found that she needs to look for availability in the T bucket for Saver Y and U bucket for Saver C (not through her typical award searching). They then have to put the itinerary on hold for 48 hours to allow time for EI to ticket their segments. I have to call back in 24-48 hours to ticket it.
If you have trouble with agent trying to make it work, let them know the above.
I wish I found this out earlier when I was trying to get some trans-atlantic EI flights and the agent was telling me she could not see the availability I had online and gave up. If you get that message, then explain to them about the bucket mappings.