If anything I think that they would get in trouble for having iconography from the movie without permission. Like the iconography on the shield. Unless that is what all spartan shields looked like, I do not know much about them historically.
According to dictionary.com one of the many definitions of mercenary is: hired to serve in a foreign army, guerrilla organization, etc. With this in mind one could say that he founded his own guerrilla organization in the context of the movie, again I do not know much about him historically, picking the best 300 and doing what they do best.
Seems like if that is what they would get in trouble for. I remember JMD had the first version of their 54mm daemonette and GW pounced on their ass for it even though there was no actual GW visual references, in my opinion. Not like it was covered in slaanesh symbols. I think that any model that needs a crab arm and horns should have one without GW throwing a fit.