Sometimes they say that. Most of the time though they say “yeah we conducted an airstrike and killed X number of Hamas militants.”
And of course Hamas says every single time “nope those were innocent people just going about their day.”
Some of them have to be Hamas, right? So, in my view, they have less credibility. Denying their own existence is part of their strategy of martyrdom. If they admit Israel really did kill a bunch of Hamas soldiers, that doesn’t push the right narrative for Hamas and Iran.