Surely though, it's not really 'acceptable' in a serious bit of research.
I don't see why it should be unacceptable to quote information from a person who prefers to use a pseudonym and wants to remain anonymous - artistic and literary material is frequently quoted as anon. If the information is accurate or worthwhile it will stand or fall as such. Seems to me that it is common courtesy to respect the author's anonymity and to treat his or her pseudonym with the same respect as one would their 'real' name.