I think the question can be taken seriously. Is a UEFI BIOS likely to interfere if ExitBootServices is not called?
No one can give you a guarantee. You'd have to test it on real systems. But here are some things to watch out for:
- System Management Mode interrupts and ACPI System Control Interrupts (link) would transfer control to the UEFI BIOS and could lead to unexpected behavior.
- For servers, the BMC (link) would likely also behave in unexpected ways
It bears repeating: calling ExitBootServices does not mean the OS forgets all about the UEFI BIOS. The Boot Services are no longer available after that point, but the OS still accesses the UEFI BIOS
when needed. Also, the things I mentioned above demonstrate how effectively the UEFI BIOS can assert itself when it wants something.