Chris, it is very difficult to be a vegetarian without eating carbs, perhaps even dangerous. You need to get enough calories and without the calories from animal fats (paleo eschews vegetable oils other than olive or avocado or the like) you will simply not get enough to sustain yourself, unless you eat carbs. The calories from fats are what replaces the calories lost from taking carbs out of the diet.
Technically any legumes (beans, lentils, peas) are not allowed in the paleo diet, because of problems associated with the enzymes in legumes and because they cannot be eaten without proper processing. However, unlike grains, there is less resistance to legumes and some people eat them in moderation.
Carbs are necessary to lower because without lowering carbs you cannot switch your metabolism over to the ketogenic process, which works in the absence of carbs; your body will automatically utilize the carbs because it is fast energy. The paleo diet and fitness routines are based on the ketogenic metabolism.
Part of the problem with protein from vegetables is that the body cannot get at most of what is there, even with plant-sources of protein that are as complete as those of soy or quinoa. The amino acids remain locked within the food source by the time it gets to the intestines. This is why the waste matter that is finally released has considerably more mass from vegetable sources than meat sources.
Fish, as a paleo-approved food, is an excellent source of protein and fat, especially because deep water, "blue" fish carry very healthy amounts of Omega-3 fats... the kind you want to increase in your diet. Many people live exclusively on fish. Here in Japan getting good variety in fish is very easy, but it may be more difficult in countries where fish is less popular.
Oats are carbs and if you want to go truly paleo, supposed to be forbidden. If you read the forums in Mark's Daily Apple, though, you will see that a lot of people have a very hard time giving up oatmeal.