The article is paywalled, but what I can read of it refutes your claims. It states that, according to (presumably Israeli) intelligence: around 10% of all of its Gaza staff have ties to Islamist militant groups

10% is a lot less than most, and that's the very broad category of "ties to militant groups", not actual Hamas members. What qualifies as a "tie"? Being related to or knowing someone in Hamas, or having to deal with them, given that they operate in Hamas territory? And "Islamist militant group" is a much broader category than just Hamas.

For example NFAC [1] is a militant group, yet it has committed negligible violence (allegedly only by ex-members, not current ones). Are they including NFAC-equivalent groups under "Islamist militants"?

[1] https://en.wikipedia.org/wiki/Not_Fucking_Around_Coalition