Is the monkey the only hardware engineer you can hire?

If an employee is level 5 in Coder, Writer, Designer, and Sound Engineer, you can then train them as a Director or Producer.

If they are level 5 in Director and Producer as well, you can make them a Hardware Engineer.

The limiting factor here is that after so many level-ups, their salary will be very high (2 million dollars or more).

As far as I know, this is the only way to get a Hardware Engineer early in the game.

One way to get a hardware engineer is to level an employee up to level 5, then change their job to something else (I would assume to something that's not already level 5). Then, level them up again to level 5. Keep doing this process until hardware engineer shows up on the list of job changes.