“We'd need to hire an immigration lawyer first” is the objection that stalls everything. For an agent-based O-1 engagement, your existing counsel can cover the ground.
Immigration counsel becomes essential when you are the petitioner — the H-1B world. Here the petition, itinerary and USCIS correspondence live with the authorized agent on the candidate side. What touches your company is a one-page, non-binding interest letter and, eventually, an ordinary offer to a work-authorized person.
Attorneys with questions can reach a team that has run agent-based O-1 practice for over fifteen years — request the call and say it's counsel-to-counterpart.