Not necessarily. It depends on how much scripting you want to do. The IR blaster does have to be able to receive Wi-Fi commands.
I personally have the harmony home hub, and like it a lot. At the current level of integration, the Harmony remote can toggle some of my Smartthings-controlled lights, harmony and smartthings have some integration through an IFTTT channel, and smartthings motion sensors can trigger harmony activities.
There is a new Harmony/Smartthings integration still in beta. The beta testers who have discussed it on the forum seem to like it a lot. It expands the two-way integration. The last announcement on it was that it had gone over to harmony for their approval. So that’s something to look forward to.
If you’re techie, we do have a number of community members using the global cache IR blaster, but it does require either a paid monthly service app like roomieremote or writing your own scripts (not just smart apps). The following topic discusses some of those projects:
So definitely you can have motion sensors trigger a television and lights to come on when smartthings is part of the mix. Which method you choose will depend on your own personal preferences as far as whether you want to do coding or not, and how much you want to spend on other devices.