Yes. Any mechanism that can modify the data is supported. In order to support External APIs with FileMaker Server, it is necessary to install the plug-in on FileMaker Server.
There is one extra requirements for all External APIs, and one limitation related to Instant Web Publishing.
The extra requirement is that if you keep the AuditLog table in a different file than a particular database being accessed, the Account and Password used by the External API to access the primary file must also exist in the file hosting the AuditLog. This isn’t required from within FileMaker Pro.
The IWP limitation (as of 1v1) is that records can not be deleted by users through an IWP connection. That is, the plug-in will return a False to the Limited deletion condition, hence preventing a user from deleting a record.