Not all diesels use glow plugs or air heaters to start. Depends on the design of the engine. Ones I can think of off the top of my head or have had experience with:

1960's GMC V-6
All old Detroit Diesel 2-cycles
Caterpillar 3208 V-8 (along with other series)
John Deere Diesel tractors
And many many more

Many brands do or have not used glow plugs. Most of time engine block water heaters are used for cold weather starting.