Given that Sarah Huckabee Sanders said the person should resign, it certainly seems like she's willing to accept that this source is an actual member of the administration:
https://www.msn.com/en-gb/news/politics/sarah-huckabee-sanders-slams-gutless-anonymous-source-for-bombshell-nyt-op-ed/ar-BBMVqbf
1) Given that there are literally millions of people employed by the federal government, it's certainly possible that she's a "member of the Administration" in
some capacity. I'd say almost a certainty. However;
2) Whether or not the person is employed by the federal government isn't the point. The author may well be a federal employee, but be ascribing to himself/herself access or knowledge that they do not possess. It would hardly be the first time someone tried to make themselves sound more important than they really are. Again, I'd bet my last buck that the stuff about the cabinet removing Trump under the 5th Amendment is bogus.
Sanders saying that whomever it is should resign is
not an acknowledgment that the person has a major position within the Administration, or that the things they claimed happened are true.
That's the relevant point.