That was a good question Jackie, and as Chris explained, it is good training to train a dog to view the helper as an adversary, and not just see the sleeve as a tug toy. Early in the training phase, many dogs get very equipment focused and that is normal and expected as the dogs are started out with very little stress, and the tug/sleeve is first introduced as a prey item - but to achieve your goal of building the dog's confidence, and testing his courage and willingness to engage, you have to get the dog "helper/threat" focused.
For example, here is a pic of my mixed breed being worked:
Notice that the sleeve is behind her, yet all of her focus in on the "bad guy". (Real Schutzhund people - as opposed to wannabes like me - are welcome to jump in and further comment or correct). He is advancing towards her in full frontal pose, with direct eye contact and a threatening look on his face. The distance between him and Keeta is very small, yet she meets his advance fully by pulling towards him, continued barking, keeping the line taught, and returning the eye contact without missing a beat.
At this point, many dogs will be overwhelmed by the proximity of the threat, and will back away, and/or go for sleeve on the ground as a safe place to be, as getting the sleeve has always been the release of the stress.