Heat oil in heavy medium saucepan over medium heat.
Add onion; sauté until soft, about 4 minutes. Reduce heat to low.
Add cream, cream cheese, Parmesan, and Gruyère.
Whisk until smooth, about 3 minutes. Stir in nutmeg. Season with salt and pepper.
Remove from heat.
Combine potatoes, 6 cups water and salt in large saucepan. Bring to boil over high heat. Reduce heat to medium and cook until potatoes are just tender when pierced with skewer, about 6 minutes.
Drain.
Transfer potatoes to bowl.
Add olive oil and parsley; toss to coat. Season to taste with salt and pepper. (Fondue and potatoes can be prepared 1 day ahead. Cover separately and refrigerate.
Whisk fondue 5 minutes over medium heat until melted and smooth. Reheat potatoes in 350°F oven 10 minutes.)
Place potatoes on platter. Spear each with skewer.