It was suggested to me on another question that, "Yes" we can cite science in our answers to Christian question but one person suggested that all science matters should derive from Christian sources. Is this true? If science is brought up, should it only derive from a Christian source?
I don't know what you mean by "Christian" sources. Oftentimes, I search my library's databases for academic peer-reviewed journals regarding Religion. The journals themselves may be scholarly, but it's important to remember that they are written by people, and people are not perfect, even if they have a PhD in Theology or Biblical Studies. Likewise, if you're citing scientific information, I'd highly suggest that you search your library's databases for academic peer-reviewed journals regarding Science or a specific scientific topic. The last person I'd cite is some Joe Schmoe on the street with dubious credentials and a shady professional/academic history. I do not think that the religion of a person should matter in regards to science. As long as the scientist - be he Christian or Jewish or Muslim or Buddhist or what-say-you - is trustworthy and conducts significant experiments or observations or contributions in whatever field, I'd think that's good enough.
Questions about science are off-topic here. Questions about doctrines related to science are on-topic. To answer what Christians believe you have to use Christian sources in most cases.
A question here should be about "what does the christian group X believe" and not about "is X true?". Anything else would distract from the purpose of the site and would also be rather dangerous as the expertise of the community lies with Christanity, and not with science.
I think this would depend on why you are citing science in the first place.
In order to answer questions, Christian sources are required. Hand in hand with this, questions are required to ask something about Christianity!
Therefore an answer that cites no Christian sources and presents no Christian position should never be warranted on this site. If you feel such would answer the question, either the question doesn't belong in the first place or you are misreading the gist of the question and only picking up on some background detail.
On the other hand if the gist of your answer does teach something about Christianity, it is possible to cite all sorts of sources for various purposes. I could easily see the usefulness of citing secular science in answer to a question that asked about the relation of some doctrinal position to some scientific case. The difference being the non Christian data would not be the substance of the answer.