Hello Tokoro,
yes, SEOTOASTER supports single core for multiple websites operations.
Run a full install for your core. Then run another install for each website you want to run off that core. During the install process, you can specify the path to the core files. Specify then your initial install path.
SEOTOASTER will install only the necessary files/procedures to run your additional website, and you will be able to run upgrades from a single core.