In the hardware vertical YC has also partnered with Bolt [1][2][3], but that seems to be a partnership rather than acquisition, and I'm not sure if Bolt considers themselves an accelerator.

[1] https://medium.com/@BenEinstein/bolts-partnership-with-y-com...

[2] http://blog.ycombinator.com/yc-for-hardware

[3] https://www.bolt.io/