Using a micro to control a VCO / PLL is not only possible: it can also add additional enhancements that are much more difficult to obtain using TTL or simiar logic. You can, for instance, add a rotary encoder to set the frequency and add accelaration in the frequency selection, based on the speed the encoder is rotated, select the step size (frequency grid), display frequency and S-signal on a (graphics) LCD, etc. If ever you are going to design a receiver or transceiver yourself, look for the serial-programmable PLL's available nowadays. They are very easy to implement, both in hardware and software, and offer a lot of nice little features not found on the older parallel programmable types.