Yes, that works fine, provided you setup all of the appropriate Phase 2 entries in IPsec and routes in OpenVPN.
For example, your IPsec tunnels would need to have phase 2 entries such as:
Site A<->B: P2 for A-B, OpenVPN-B
Site A<->C: P2 for A-C, OpenVPN-C
OpenVPN: Local network set for A, B, and C
And if you want B and C to reach each other through A, you'll need additional P2 entries to cover B-C / C-B on the appropriate tunnels and in the proper direction.