It is only appropriate if you can adequately explain why the answer can only be obtained through a visit to the vet.
For instance if to find the answer will require lab tests, x-rays, and/or other complex medical procedures that should be explained. If you are not able to say what will be required to answer it then it is much better if you leave the question unanswered so that those who do know can answer.
Many times the first answers in if they sound about right will get voted up and drown out responses that come after. If you can not provide a quality answer that adequately explains the situation then leaving the question unanswered lets the experts focus on those questions to help resolve the problem.
In addition people are coming here many times hoping to avoid a vet bill but still take care of their animal. If all they here is a vet can answer that, they will tune it out. If you explain why they need to go to a vet they are more likely to take them to a vet so they can get the care they need.
And finally there are many things being referred to vets that do not really need to go to the vet. Many of the experts here have the knowledge of either how to answer, or where to get the answer from. Everyone knows they can go ask the vet, but running to the vet for every little question is not only expensive it is wasteful. It is similar to running to the ER every bump, scrape, or splinter. We should try to help where we can.
Here is a perfect example:
In this version it basically just says you need to see a vet.
In this version it explains why you need to see a vet.
The first version was really noise where the second one brought the explanation home which should be much more helpful to the OP.