Are Samsonite gears compatible with modern Technic gears?
They are not compatible, the teeth are completely different.

Notice that the red old gear has 9 teeth and is the same size1 as a current 24-teeth, as illustrated by below:



The axle hole however is compatible, so you could have a construction using both types.

1. Actually, the distance between axles to have two of these red gears mesh is the same as the one required for two 24-teeth ones (60 ldu).