Some vegetarian-like diets (such as pescatarianism or ovo-lacto vegetarianism) allow for foods that some vegetarians would not consume. Are questions about such diets topical for Veg*.SE, or should the site be more restrictive?
There is no obvious "correct" way to define vegetarianism.
Ask: are they become more vegan (the ethic), or less vegan?
Yes, but barely, and a bit provocative: "I sometimes eat chicken but am making an effort to get half my protein from plant sources. What plant proteins complement chicken?"
In my personal ethics and opinion, yes: "I am mostly vegan but sometimes splurge with fish. How can I follow best practice and keep my fish consumption ecologically sustainable?"
Probably not, since the focus is on the non-vegetarian aspect of the diet: "I keep mostly vegan and sometimes eat fish. Can I now stop consuming flaxseed oil?
No: "Does kale go well with ham sandwiches?" (Presence of vegetable does not mean vegetarian).
I think we will attract more users if we keep the exchange open to anyone asking about vegan or vegetarian eating/living, whether or not the asker is veg*n in the entirety of their life.
If someone asked a question in Stack Overflow about how to solve a problem while programming in Java, no one would care how they solve the same problem in PHP. Different languages, different conversations.
So long as the questions being asked here are about veg*n eating and living only (not, as others have stated, adding vegetables to meat dishes) I don't think it matters if the person happens to also eat meat or other animal products.
This will have to be evaluated on a per-question basis because it's not a well defined topic. Pescatarians eat fish, which are animals and are "made of meat". The reasons why someone might eat fish will vary but are irrelevant. The purpose of the question is what will define if it is on topic or not. Questions about the advantages and disadvantages of eating animals are on topic in this website but one would have to ready them selfs to the idea that the vast majority in this website will defend and back the argument that you don't need fish to be healthy and give you an array of alternatives and reasons why that is true.
So in the end, even if we collectively allow this kinds of questions about "vegetarianism-not-really", there will be only a few that won't be downvoted to oblivion.
Vegetarianism is practiced in a variety of ways. Including being only practiced at particular times or including some exceptions that strict vegetarians would not agree with. I think anyone interested in any aspect of the lifestyle should be welcome to discuss it.
Many of these diets share similar ethical and health concerns to vegans or strict vegetarians. They should be able to ask about these aspects.
Obviously, this is not the place discuss omnivorous diets but those with restricted meat/dairy/egg intake may still benefit from participating in a largely vegetarian community. For example, if someone is not vegan but is allergic to eggs or dairy, they may still ask about substitutes and health risks.
Could "is this dietary/consumption practice seeking to relevantly restrict or eliminate the use of all or some animal-derived food and consumables and/or their negative impacts?" be a reasonable guideline for the "outer limit"? It would include the flexitarian that has gone mostly plant based, it would include other semi-vegetarians that are serious about less-cruel sourcing - and create an opportunity to educate people about some well-meant but well-perverted labelling. It would keep the "chicken only because less fat" crowd well without.