GYM*RAT, I get asked that question more than I hear, "That you for your service!"
None of the family members are agents and they all abide strictly by the rules and usually only bring other family members into the movie biz (temporarily) if the director says something like. "Do you have a family member who can do this ........?"
And that is not a frequent request.
But both Rich Piana and Orvile Burke have played small roles in the past Planet of the Apes series (without my assistance) and I doubt that they had agents, so it is possible to get minor roles if you are in the right place at the right time.
But absolutely no one would recommend anyone that they did not know personally because if that person screwed up on the set or simply did not show up on time ..... it would be a bad reflection on the cast member who recommended him/her.
I'll do some checking to see if the SEG (Screen Extras Guild) is still in existence but I believe that that organization has been long gone.
At present I am only familiar with SAG.
I think that Adonis and Marty have been successful in getting small roles recently and they may want to offer further information on this subject.
If you manage to get one job on a movie set, there is a good chance that you'll be offered others.
In the past I have argued with others on various internet boards about the 'impossibility' of getting work within the movie business.
I disagree entirely.
It's difficult but .... NOT IMPOSSIBLE!