Vegetarian or not makes no difference to weight loss (though you may need to watch protein intake a little more closely to minimize muscle loss). Log your food, have a reasonable deficit (not *too* big) and you can do it!

Yes! I did this with my first pregnancy...became vegetarian the day my son was born and on his 18 month birthday I had Pizza Hut meat lovers pizza. 18 months of no meat, along with exercise 4/5 days a week worked for me

I'm also pescatarian, but usually only eat fish when we eat out. I also try to eat mostly whole foods and pass on packaged and processed as much as I can (and resist the Goldfish crackers that seem to find their way into the house for the 2 year old). I had a week where I was eating more bread but still keeping to my calorie limits and the scale didn't budge. Could be a coincidence, but anything that motivates me to make better choices is a plus!
I will add that it is just as possible to be unhealthy on a vegetarian diet as a omnivore diet, but sometimes making any change in diet forces you to think more about your food choices, and that can have a really positive impact. When I started eating vegetarian I had to learn new recipes, so I tried to choose healthy new recipes. Good luck, and let us know what works for you!