The base of the 100MHz oscillator is held rigid by the 2n2 as it has a very low impedance at 100MHz.
I have designed over 25 RF transmitter circuits like the one shown (except all of mine have a self biasing oscillator stage) and sold over 100,000 kits.
An electrolytic is not needed on the supply rail as the audio is being injected into the RF stage and the current taken by the microphone and audio stage is very small in a well designed circuit. It is an unnecessary component.
However a 22n on the supply rail will improve the stability and increase the output of the RF stage as this stage is drawing heavy peaks of current.
The reason why the two stages should not be DC coupled is as follows: The oscillator stage needs to be self-biasing for stability. If is connected to the collector of the previous stage, this self-biasing is negated.