In additon to th Cat 1 status for Nigeria, Arik would need to apply to the FAA for a 129 certificate, this would allow them to fly into the US.
I have friends in training with Arik/Hifly for the flight attendant positions. The are employed by a Crew Leasing firm in the US, being trained by HiFly and will wear Arik uniforms! The all have FAA issued flight attendant licenses/certificates. From what I have been told, Arik bought the planes, dry leased them to Hifly and then wet leased them back.... I could be wrong...