Depends (corrected)
Some consider Thousand Island to be a derviative of Russian as it is commonly formulated ("a mixture of mayonnaise and ketsup"). Older recipes do not use mayonnaise and may or may not use tomato paste, so they are not as similar to Thousand Island.
I don't generally have mayonnaise so the recipe I used doesn't call for it, nor for tomato paste, but only oil, lemon juice, red wine vinegar, garlic, onion Dijon mustard, chili sauce, salt and pepper. It's quite good and it's reasonably thick made in my little mini-prep food processor - it's been hours and it shows no signs of separating.
So basically, it's hard to compare. Thousand Island's origin and formula are well identified, but what Russian dressing is is quite another matter. Some even say it was called "Russian" because it originally included caviar.
