I oppose anything using the Nix/NixOS trademark from accepting a defense sector sponsorship.
A conference accepting a sponsorship from any company is not a politically neutral action; it is an explicit endorsement of that company. That’s literally the entire reason companies sponsor conferences so that the conference will endorse the sponsor (such as by prominently emblazoning the sponsor’s logo, for example) and improve the sponsor’s standing/image in the community. There is nothing politically neutral about that.