I have not much experience with Automator (so far Otto and me did not become friends), but there is also a built-inshell command for executing Automator workflows that can be used from within AppleScript using «do shell script».
In order to use this command, you need to re-save your Automator apps as workflows (not as applications):
set wfpath to "DandyDisk:Users:martin:Desktop:test.workflow"
set qtdwfpath to quoted form of POSIX path of (wfpath)
set command to "automator " & qtdwfpath
set output to do shell script command
Here on my systems, using this technique results in workflows being processed one after each other.