I think maybe you mean "not intended" instead of "proper". However, I don't see much other purpose for the command line scanner if it isn't to scan files and get the results. What would the command line scanner be for if not that? Wanting it to be efficient and work with the already loaded scanning system is hardly anything special -- things like this have been around for decades.
This is a "server product" right? It should support automation and integration into local tooling...
Can you point me to the ESET API documentation? Contacting a distributor is not normally how ones get information about APIs, nor an approach that I would deem useful. It would likely take weeks to get any form of answer.
The only documentation I can find is related to the Server_API for interacting with the management center, which is not at all useful for what we want. Is there some other API hidden away?
Also, using an API is highly non-flexible or generic for integration into other tooling. Basically we would end up writing a command line scanner tool to scan the file via the API -- which sounds an awful lot like what's already there...