Thank you all for your great suggestions! I'll be sure to report back when I find the right formula.

I was initially going to say tahini but from the pic it looks more like peanut butter. I would go with that, plus sesame oil, garlic, chili powder, rice vinegar and miso. Use a blender to get it to emulsify=creaminess.

@AntoniaJames.
If you're using that as a salad dressing. Use lemon and lime juice as the acid base. Add a clove of garlic. A bit more sugar--to taste.

/I really need to quantify some of my suggestions...I'm very, very, bad at writing down recipes with proportions.

I'm with Sadassa_Ulna on this, in that I intend to go whip up what Sam1148 has suggested, ASAP. Wow. Great question, Kristen. ;o)

Ahhh...here's a good starting point. Goma sesame dressing. Common with Spinich and noodles.
There are other recipes out there with the tech...this link is a pre-made product. But might give you a better idea of texture and color.

http://www.nihonshokken.com/en/goma_dressing.html

Yum, Sam1148! Even if that isn't Kristen's dressing that sounds great ;)

I'm guessing toasted sesame seeds. Ground to a paste in a mortar and pestle.
Added to a dressing base...and probably a touch of rice wine vinegar.
A touch of soy (or Ponzu), sugar (or mirin), a bit of dashi stock and a bit of dry mustard to bind...and whisked in a blender with light veggie oil drizzled in like a mayo; to make a creamy dressing...almost mayo like.
(I'll bet it does has a some lemon or lime in it as back tone).

It is more than the sauce, it is how the daikon is "shredded" It is not shredded as you may think. It is first cut very long continuous "peel" of a piece of daikon with a special knife (usuba) using a special technique. The long peel is rolled up again, looking like the original piece of daikon and wrapped in a damp cloth. You then can create your julienne or shred, as needed. How any vegetable, fruit, meat, etc is cut can change the taste, texture, mouth feel and how the end product will perform. But, the sauce is important too.

Thank you guys! I should have specified that the creaminess seems to be from something like miso or tahini, rather than dairy or mayo. It's opaque brown and doesn't taste of ginger or lemon. It's an enigma. Soy sauce or tamari is definitely involved. I just noticed the menu calls it "sesame dressing" -- and I found a photo on Yelp! http://bit.ly/hptFie

I'd say the restaurant seems pretty authentic (KILLER ramen -- it's called Minca if you're ever in NYC): http://www.newyorkramen.com/

And yes, I plan to interrogate the staff the next time I eat there, but usually I order takeout (i.e. my dutiful boyfriend picks it up).

AJ's ideas sound good. Does the shop serve more or less authentic Japanese foods? If so I would rule out buttermilk. Perhaps that Kewpie Japanese mayo contributes to the creaminess? The sesame oil sounds like the nutty . . . nuttiness. Does it have a ginger or lemon flavor? What color is it? Have you thought about asking the shop's people what is in it?

That doesn't sound evil at all. It sounds very intelligent. Okay, nutty: possibly a touch of sesame oil plus a little dab of peanut butter. Salty, well, that most likely would be soy or tamari. The creaminess could well come from peanut butter, but if the dressing is kind of white looking, the secret ingredient might be mayonnaise. It's entirely possible that they're using ranch dressing . . . . if I were making this, I'd use buttermilk, and I'd make it in a blender. Please post the recipe when you've perfected it!! Thank you. ;o)