Can an NMLS Administrator also have an NMLS number?

No, except for very small institutions.

What would the definition of "very small institution" be?

1007.103 Registration of mortgage loan originators.

(e) Required covered financial institution information.

(1) Covered financial institution record. (i) In connection with the registration of one or more mortgage loan originators:

(F) Name(s) and contact information of the individual(s) with authority to enter the information required by paragraphs (d)(1) and (e) of this section to the Registry and who may delegate this authority to other individuals. For the purpose of providing information required by paragraph (e) of this section, this individual and their delegates must not act as mortgage loan originators unless the covered financial institution has 10 or fewer full time or equivalent employees and is not a subsidiary

http://www.bankersonline.com/regs/12-1007/12-1007-103.html