I think CoH 2 use Steamworks servers since beginning. No changelog talk about servers migration.
Little history about Steam features:
- 2013/11/13: Public chat added.
- 2013/12/10: Steam Workshop Integration
- 2015/06/23: In-Game store and User Generated Content (UGC) Hub
- ...
cf. https://www.coh2.org/topic/4307/coh2-changelog