Have harmony ultimate pause tv when motion?

You have to first create a harmony activity to pause. That will then appear as a virtual switch to smartthings. Then just have the motion sensor trigger the virtual switch.

The official SmartThings/Harmony Integration only works on the basis of activities, it does not expose individual buttons on the remote.

If you want granular button control you have to take a different approach and use an unofficial Integration. But this is technically much more complex.

[RELEASE] KuKuHarmony - DTH and SmartApp that support to control devices in Logitech Harmony(using Harmony-API)