Yeah, it's a log of all the software that runs on the server. If you trust the secure boot process then you trust the log describes its contents.

If you don't trust the boot process/code signing system then you'd want to do something else, like ask the server to show you parts of its memory on demand in case you catch it lying to you. (Not sure if that's doable here because the server has other people's data on it, which is the whole point.)