Simple answer: no.
Harder answer: yes. You can - after the map loads and creates the starting units for each race - REPLACE every unit near the starting location of a certain player by the units you wish to spawn. The trigger would look like this:
Game - elapsed game time is 1.00 seconds
Unit group - pick every unit in (units within 750 of (player 1's starting location)) matching: (Boolean - (matching unit is a worker) equal to true) and do action: replace picked unit with a Uberpwnslave
1) this trigger leaks a unit group
2) Notice how the undeath only has 3 worker units at the start and 1 ghoul, while other races have 5. In addition to that trigger, you should first check the race of the player. If it's undeath, remove the 3 workers + ghoul and create 5 UberPwnSlaves for the player, else simply replace the workers.