Yes as far as immigration is concerned. An L-2 spouse is employment-authorized incident to status and may work for any employer, including a dealer. Children in L-2 status may study but not work.
Her employer can be anyone; her status still depends on his
The spouse of an L-1B transferee is admitted in L-2 status and, under current policy, holds employment authorization by virtue of that status without a separate application. She may take a job at a dealership, at a school or anywhere else, and she may be self-employed. The authorization is derivative, so it exists only while his L-1B and her L-2 remain valid, and it would end if he changed to another category or his petition lapsed.
She should keep her admission record accessible for an employer's verification. There is no immigration objection to her working for a dealer that also receives his technical support, but the company should keep her employment entirely separate from the dealer-support arrangement so that no one confuses her job with his controlled placement. Their children may attend school at any level but are not employment-authorized, and each ages out of derivative status at twenty-one.