Regarding honoraria received, unless the museum who employs this
individual paid for that individual's education, I would say
that any money received belongs to that individual alone. There
is not a conflict of interest unless, as you say, the work in
question was accomplished on staff time or there was a
pre-arranged agreement stating that the individual would not take
any paid work outside of the institution.
I know of numerous curators/museum profesionals who do work on the
side, often for smaller museums and publications that cannot
afford to employ a full-time person--me being one of them.
Anyway, after taxes, it's a pittance!
John Handley
San Francisco