It really depends on which community you're talking about. If you mean the wider community, then yes - a well-informed answer that increases the individual's - and any other readers' - scientific knowledge on biology is very useful. The layman has become if anything comparatively more ignorant in the 21st century, despite greater access to scientific information, as the depth of scientific knowledge has increased and scientific terminology has become almost a language unto itself.
Questions like 'is this hippo-croc a real creature' are not necessarily a joke, but rather a result of profound ignorance - replacing that ignorance with knowledge, especially a general-case answer that isn't simply 'no', is unlikely to be negative to the cause of biology and science in general.
If you mean 'useful specifically to biology students, researchers, and academics', then no. It is very unlikely that anyone enrolled in a degree, engaged in research, or teaching students will gain any significant knowledge from an answer to that question.
So really, it's a question of audience - to whom do you want the information recorded on this site to be useful?
Given the search capabilities of the site and the disparity in terms used, it doesn't seem to significantly harm anyone to have these sorts of questions being answered. As long as the normal duplicate question stack exchange guidelines are followed, building a body of knowledge that informs not just the erudite but also the ignorant seems morally superior to the alternative.