Yes. In Scotland a Civil Marriage ceremony can be conducted by a Registrar or an Assistant Registrar in any licenced location, including Culcreuch Castle Hotel.
This is similar, for example, to being married by a Justice of the Peace in the United States.
A religious wedding ceremony may be conducted at any suitable location by a minister, clergyman, pastor, priest or other person entitled to do so under the Marriage (Scotland) Act 1977.
The Castle's Weddings Office holds a list of local ministers for all the main religious faiths, christian and non-christian.