I'm quite sure the answer is: No.
When using the according database utilities, it's possible to use a configuration file to specify parameters. And it's possible to use DBFHIDE to obfuscate an configuration file to hide certain parameters.
Sometimes it would be handy when the same would be available with the DBTools API.
But from the documentation, such a parameter seems unavailable. (And I guess it might be difficult to implement as the DBTools structures have different members for certain options whereas the command line tools just use one single command line to specify all.)
Is there something I have overseen?
You are correct - the answer is no.
Dbtools is a library with a number of interfaces to perform various operations - create database, backup a database, initiate a sync, etc - and each interface includes all of the parameter that it needs to complete the operation. Most of the command line tools - e.g. dbinit, dbbackup, etc - are simple programs that read their command line parameters and then calls the associated dbtools API with the corresponding parameters from the command line. The reading and parsing of the command line parameters that use the @file syntax is a function of these simple programs and is not a function of the dbtools library.
Put another way, the dbtools API has no concept of "command line parameters" and hence does not know how to parse the parameters if they were to be put into a file.