Can an entertainment manager also be a talent agent?

Yes, in California, nothing prohibits a talent personal manager from also getting the requisite license and bond to be a talent agent too. I know lawyers who are also managers, and lawyers who are also agents, since a legal background can be helpful to both jobs.

In fact, some lawyers and managers get an agency license just to get around the archaic and widely-criticized Talent Agency Act, California Labor Code sections 1700 et seq. That law bans people who aren't themselves licensed agents and aren't working in conjunction with licensed agents from doing certain things, such as booking live shows and shopping and securing songwriting deals (recording deals are specifically exempted from the TAA). or shopping literary deals for screenplays.

One concern about being and acting as both personal manager and agent, or being both a lawyer and agent is the potential conflict of interest and ethical conflicts, since the duties and regulation of each job is different.

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.