I had read about this place on happycow and stopped in to try the vegan dog, October 2012. Here's my Underdog review.
It's a tiny little shop with 1 or 2 small tables inside and a bench outside for seating. The interior is colorful and you order at the counter. The chalkboard menu above the counter shows an "organic sausage" list, then a vegan dog list, then sides and drinks list. The vegan dogs come in your choice of wheat or white bun, and you help yourself to the toppings bar which has mustard, ketchup, sauerkraut, chopped raw onion, relish, and hot sauce.
I got the basic vegan dog, $3.99. It's not a small soy weiner like what the tofu-pups sold in stores -- it's a thicker and more flavorful. It came piping hot between whole wheat buns, and I topped mine with sauerkraut, mustard, and hot sauce. Tasted good.
I'm not a fan of the hot dog, though, because this food is just too salty for me even before one adds on the mustard and relish, etc... but Underdog is still a fair choice for vegetarians and vegans who want to get a hot dog cheap and quick. $3.99 to $4.29 each.
The woman at the counter told me that their sides and desserts are always vegan suitable. On this day I saw cole slaw, potato salad, and one kind of cookie.