SCUMM is (was) the scripting language used to implement game logic in the various Lucasfilm/Lucasarts games. The engine was referred to as SPU (SCUMM Presentation Utility). So it's not like the whole engine was written in SCUMM. Audio, graphics, video, fonts, walkbox handling etc was in native code, of course, and especially in the first games a lot of stuff was hardcoded in the engine.

It doesn't really make sense to call it a SCUMM emulator, ScummVM has a reimplementation of the whole engine.

Of course there's also other engines in ScummVM, some based on the original source kindly donated to us by the developers, but most created by painstaking disassembly.

ScummVM does have emulation for various pieces of audio hardware but that's the only part I would consider emulation.