Yes, it's a good tag, but we might want to consider renaming it.
Let me try to say my views here.
This is definitely a useful tag, if you're inquiring specifically for scientific studies. It's not quite as clear-cut on the current two questions though.
Are there studies that have determined the main reasons people stop being vegetarian?:
This fits better than the other IMO, as the last sentence reads "Are there studies [...]", but the rest could be clarified. This probably belongs here, but I don't think research is the best name for it in light of this. Maybe studies or scientific-research?
What are the personality traits of those most and least likely to go vegetarian?:
This one is actually really broad/opinion based IMO (it's a fine line in this case). I like what @Zanna said:
I think if would be very difficult for studies to account for differences between cultures (the study itself unavoidably emerges from/is produced by some culture) but answers could summarise studies from different areas so I think this question is probably answerable
TL;DR: answers are gonna be really big and a summary of a bunch of studies, but the question is answerable.
(thus I haven't voted to close)
Also, I'm not sure the tag is entirely needed, because any answer that doesn't cite sources is a Bad Answer™ and probably entirely based off of personal experience.
TL;DR: Keep it, though maybe rename it, and clarify its usage in the tag wiki.