Heat grill over medium-low heat and oil the grates well.
Dice potatoes into bite sized pieces. Depending on the size of your potatoes, this could mean halving them or quartering them. In a large bowl toss potatoes with 1/4 cup olive oil, 2 tsp kosher salt, 1/2 tsp smoked paprika and black pepper to taste.
Put the seasoned potatoes in the grill basket and grill over medium-low heat until browned on the outside and fork-tender, 25-30 minutes.
While the potatoes cook, make the dressing. In a large bowl, whisk together dijon mustard, greek yogurt, mayonnaise, white wine vinegar, garlic, 1 tsp kosher salt and black pepper to taste. The dressing should be thick, but you can add 1-2 tsp water if it seems gloopy. Set aside.
Once the potatoes are cooked, let them cool for 15 minutes. Then toss them with the dressing, minced fresh herbs and celery. Serve warm, or chill for up to 2 days before serving.