Success!
So to recap: The new Samsung Series 9 Ultrabooks do not boot into Altiris WinPE 2.1 - after loading the initial files the laptop boots to a black screen. Further research indicates this is likely a driver issue, and none of the manufacturer-provided drivers resolve the issue.
As a workaround and to avoid disruption of our production environment, I created a bootable WinPE 3.0 USB drive. I'll document the steps below as a reference for anyone else running into similar issues.
I first created a bootable WinPE 3.0 USB drive as per this link:
http://4sysops.com/archives/build-a-bootable-windows-pe-3-0-usb-drive-with-rescue-tools-part-1/
I then mounted the boot.wim file from a working WinPE 2.1 config:
dism /mount-wim /wimfile:c:\temp\boot.wim /index:1 /mountdir:c:\temp\image
and copied the following from the WIM to a temp directory (assuming the WIM is mounted to c:\temp\image):
1. c:\temp\image\dagent (directory)
2. c:\temp\image\startup (directory)
3. c:\temp\image\windows\system32\startnet.cmd and startutl.bat
4. The contents of the root directory at c:\temp\image
I then unmounted the WIM file:
dism /unmount-wim /mountdir:c:\temp\image /discard
I then copied the boot.wim file created in the previous step to a temp directory and mounted it via DISM:
dism /mount-wim /wimfile:c:\temp\boot.wim /index:1 /mountdir:c:\temp\image
I copied the optional scripting and WMI components to a temp directory (c:\temp\package) from C:\Program Files\Windows AIK\Tools\PETools\x86\WinPE_FPs (winpe-hta.cab, winpe-scripting.cab, and winpe-wmi.cab), then ran DISM to integrate the packages into the boot.wim:
dism /image:c:\temp\image /add-package /packagepath:c:\temp\package
Finally, I unmounted boot.wim and copied it to my USB drive under the Sources directory:
dism /unmount-wim /mountdir:c:\temp\image /commit
Once this was done I had a complete bootable WinPE 3.0 environment that loads the Altiris DAgent. For specific cases such as the Samsung, our techs can boot to USB to image instead of the network.