I don't see how NVCompress would help him load DDS files that already exist into memory in an application written in Object Pascal. NVCompress creates (with compression, as the name says) images and outputs them to disk.
And nvdecompress (had to double-check the name) does the reverse. It decompresses a DDS file to disk which can be read by any software, including loading into a TImage.
In raw case it'd require storing an intermediate/temporary BMP file.
However, as nvidia texture tools is MIT, anybody can make them into a library / unit. There's already a compiled nvtt.lib in the folder, thou I've never used libraries before, and I can't advice on how to load it in FreePascal.
Well, that's technically true, yes. Just seems extremely strange to recommend a command line tool written in C++ specically meant for development in C++, when there are "code-only" (as in no external binaries required) native options written in Pascal...
Also, FPC is incapable of linking against static libraries that were compiled with MSVC in Visual Studio (for reasons I'm not sure of... it sure would be nice if it could!) so using the lib file would be a no-go from the outset. You would need a version of the library compiled with some form of MinGW to be able to link against it on Windows.
The most "long-term useful" option for someone who really wanted to use NVTT with Pascal, frankly, would be to simply translate the original C++ source
to Pascal as it could then be directly used in any project.