Can you explain what are you trying to do?
Why don't you use MLAG configured on the SX1012 for example?
Closing a loop between the switches will cause the RSTP to block one of the ports.
We expect MLAG connectivity to be replicate what it would like if both the switches were one. So, we need the links in between the SX1012 and the HP switch.
Once you have MLAG, RSTP is not required as long as the HP switch supports MLAG.
I would like to understand what you are trying to do here as well.