SWARM can work standalone. For all intensive purposes, you could build your own mining OS with SWARM using an Ubuntu minimal installation. The only thing required on your end is installing drivers for miners. I believe at this point most of apps SWARM use are in SWARM. However, it will not send stats/operate through HiveOS.

I have a few users that build their own miningOS using SWARM (they save money not paying for any service), but most users prefer to operate through HiveOS or SMOS. I personally am too obsessed with the metrics/performance of SWARM to spend time to build a GUI, and I prefer to avoid it because in its current minimal state it can work on many platforms with very few changes.

SWARM is complete administration, and can work on its own. The only thing required is a shell of an OS with drivers installed, and the minimum dependencies detailed in the wiki. But it will download miners, start them, and control them like a typical MiningOS would. I just have done the legwork to make it working in HiveOS and SMOS.