Are you sure of that? One most of the systems I've used with IPMI functionality (oracle and supermicro), the BMC resides in a separate chip with it's own processor and RAM.

https://www.thomas-krenn.com/en/wiki/Nuvoton_WPCM450R_IPMI_C...

Oracle uses these:

https://www.aspeedtech.com/products.php?fPath=20&rId=376