You should be fine just swapping in the chassis with the 1.1 midplane. 
We've been running M620 blades with the 1Gb Pass Through modules with no issues. The M620s have the Qlogic\Broadcom 10Gb KR mezzanine cards for chassis slots A1\A2. We have just bought some 10GbE Pass Through KR modules and swapped them out. into the same A1\A2 slots. When in the BIOS setup we get green link lights with our Cisco Nexus switch which shows a connection on the port but when ESXi6 loads there is no link (just orange light on the module). NICs in ESX are set to Auto (won't allow to force 10Gb as per VMWare).  Have tested firmware updates, driver updates, changing from the Dell Twinax cables to SFP+ and fibre but no link. If I put the 1GbE modules back in they work fine.  Strangely at one point I did get network up link in ESX running just one passthrough but have not been able to recreate it. Am I missing something as I cannot see a reason as to why they shouldn't work? This chassis we are testing on is quite old (2008) and we are using just for testing before we deploy these into our newer M1000e chassis. Could it be the hardware inside the chassis causing a problem which has subsequently been updated?    
M1000e Blade Chassis & 10GbE Pass Through Modules