Taming seems a bit brutal. It's a euphemism for conquering.

In what way are these new Lekgolo different from the ones we have become accustomed to? Have they been genetically engineered? Did their ancestors consent to the process?

: They do have a weird connection to Forerunner artifacts though.

I wonder if it's true that some avoiding eating F stuff. It could just be a convenient lie to deflect the ire of the Covenant rank and file.

It's very rare for a party in a conflict to be so generous to the other side that they take the effort to make distinctions between individual enemies. You would have to mark individual Lekgolo and observe them over a long time to ensure that there are two behaviors. Or maybe the F artifacts left tell tale isotopes in the Lekgolo bodies so that F artifact eaters and F artifact avoiders could be told apart.

It just seems like a lot of work to be able to tell the difference.

I suspect that it would be simpler just to tell a lie - given that you want to reach a compromise. You might as well just say what you want others to hear. ;-)