Yeah, OpenWRT doesn't use openssh by default - it uses dropbear. You can install openssh, if you want more features and there seem to be 2 packages - one with PAM support (openssh-server-pam) and one without it (openssh-server). PAM-less one is the one without the suffix so perhaps it's more likely you'd install that one out of the two, but only if you were trying to switch to using openssh in the first place.