Eating vegetarian along the way is easy, no problem at all if you're not picky. When in restaurants, mention that you do not eat fish and bacon, as those are considered vegetables in spain... and maybe cook your own meals from time to time, what you get in restaurants is not too healthy and rather boring after a while. Canned lentils and chick peas are available in almost every tienda. In bars, tortilla is your friend (if you eat eggs). In albergues where food is served, especially donativos, it's tricky... some will ask if there are vegetarians that evening, some will not ask but expect you to tell, and some will be annoyed if you tell them. Personally, I usually did not tell and was happy if there was something I could eat
if not, I had some emergency food in my backpack.
Regarding camping - there are not many campsites, but it's possible to camp at least from time to time. I regretted sending home my tent in St. Jean Pied de Port. Saw people with small tents at Roncesvalles, in the yard of the Estella municipal, the Hospital de Orbigo municipal and the German albergue in La Faba. In Torres del Rio there's a tiny tienda run by an old woman (close to the end of town), where if you ask you might be allowed to put up a tent in her garden. I know people who camped there (this year), and the lady was lovely. In general, if you want to camp – ask. It will not be mentioned on any sign, but if you ask, many albergues and sometimes locals will allow it for a small fee.
On the Francés you won't save much money, though – when you put up your tent in the garden of an albergue, they'll expect you to pay the same price you'd pay for a bed. The good part is, it's still extremely cheap (usually 5-8 Euros, cheaper than a camp site!), and you'll have access to the showers and kitchen, but more privacy than in a dorm room. So I think it's worth to carry the lightweight tent, even though most others here will disagree (I carried my tent for about 900kms before I got to Spain, so I'm biased).
Wild camping, sadly, is illegal in Spain, and they are serious about that. Don't try it unless you're a master of stealth camping. I met a french couple who had walked all the way from the Swiss border, doing wild camping most of the time. Spain was the first time police made them pick up their tent and leave. They told me they usually were tolerated if they did not put up a tent but slept under the stars with sleeping bag only. Still not exactly legal, but maybe a compromise.
Buen Camino, fellow veggytentigrino!