Can L2 visa holder enter US while the primary L1 holder is out of US?

If he has a valid L2, he should be able to enter the U.S. However, I recommend a discussion with the attorney who prepared the visas to avoid surprises at the port of entry. There is some confusion about the process. Foreign nationals do not interview with consulates for employment authorization documents (EADs). Those are issued by Immigration, not the Dept. of State. If you want a second opinion, consult another immigration attorney.

I assume you mean visa by EAD because consulate issues Visas, Department of Labor grants EAD. Once he has L2, he is able to travel alone.