Why be clear? – So people get the correct information collected ???
Using < > notification is standard practice or using words to clarify would be expected.
REFERENCE:
2.2. Considerations relating to DNS
"Even if Checkmk requires no name resolution of hosts, " …
WoW 
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@ andreas : Try providing actual facts backed by references to actually provide help? 
I’m setting up a LAB without DNS to demo / validate the product. The documentation also clearly stats the that defining the IP works. If you have some “Requirement” provide some solid data and references.