“Sometimes it is and sometimes it’s not.”
Use the ones that are. Don’t be so judgmental against shadchanim in general. They are far far from rare.
“My Rav actually suggested that I use one of these sites.”
Did he suggest Frumster particularly? If not, you ought to consult with him. These shadchan-free websites have many multitudes of dangers in utilizing them. I don’t think I need to enumerate the depth of this danger.