My problem was user error - I wasn't passing the output I intended to into debconf-set-selections...
I've got debconf selections working now.
The ultimate goal was do remotely install cfengine2 via a process similar to this:
#!/bin/sh host=$1 debconf-get-selections |grep cfengine2/ | ssh root@$host debconf-set-selections ssh root@$host DEBIAN_FRONTEND=noninteractive apt-get install --yes --force-yes install cfengine2 scp /var/lib/cfengine/masterfiles/inputs/*.conf root@$host:/etc/cfengine ssh root@$host cfagent -q
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