Kinda - So MS already considers many of its acquired studios as "LIC"s - limited integration companies. These studios are to be essentially left alone, not fully integrated within the XBOX first party studio lineup. Zenimax definitely falls into this category.
By creating Vault, Microsoft could do a lot of things - some interesting and some totally boring. You can create a new legal entity prior to close to begin some of the integration work so when close does happen, it doesn't take as long to get people ramped up. They could use "vault" as a landing spot for all future acquired businesses that shouldn't be fully integrated (think publishers/not developers) Vault on its own could have 0 employees prior to zenimax OR it could have a group of employees with a specific strategic mission that lines up with zenimax's importance to MS. Maybe Vault will be where games are made for multiple platforms - not just MS/PC.
M&A is fun! haha .. and complicated