Multiple laser diodes in series using a driver board
Any thoughts on how to wire these? Can I simply put the LD pins in
  series?


Not if you want to monitor the light output using the inbuilt photodiodes and use the light output value to control the laser diode current. In controlling the current for the one you are monitoring you may be overdriving another laser in series.

To do this properly you should consider driving all three independently, each with their monitor and control system.

An alternative is to decide which laser outputs the most laser light (for a given current) and use this as the controlled (master) device. The other lasers in series will be slaves and not quite put-out the same level of light.