Primarily Opinion based answer:-
Attorney or legal firm can be applicant for number of inventions in diversified filed. as it only right transfer i.e. rights are purchased and inventor is compensated for inventive subject matter. such transfer as via assignments, bonds etc.
Now comes to attorney or agent being inventor of diversified filed, Patent law as such doesnot restrict patent grant based on opinion that person has filed application in unrelated technologies. However in such case person interested can object inventor being not true inventor but evidences of not being inventor has to be produced in front of USPTO. e.g. affidavits of true inventors, declaration, misconduct of incorrect submissions etc. Keep in mind that a person can file patent in diversified field like great Thomas Edison.
I think its best to inform you that USPTO and BAR requires some ethics standard for registered practitioner to be follow rules. And I really doubt that practitioner as you mentioned will jeopardize his/her carrier by doing misconduct.
Invention is what being novel and not obvious, in fact almost all invention are based on prior arts (published), by definition if a person has conceived the invention he/she is inventor. I believe that it depends on proving the fact that if attorney has filed application based on arts or teachings which were not published at that time but later on resurface then attorney can be of incorrect inspiration misconduct. If filled application being published and based on that new invention is made which is novel and inventive, then I really doubt that attorney is at fault.