Hello, the DIA tool checks the OS version and fails out if Retail. To verify the OS, in  a cmd prompt window type   SLMGR /DLV  the returning window should tell you what the OS is. The description should be OEM or Volume channel. If it is Retail, that is why you have a failure.  If using media from Microsoft Creation Tool kit, it will install as retail if placed on a system that did not ship with OEM licensing. If installed in a VM, it will install as retail as well but the DIA tool will convert it to OEM when it captures the image. Hope this helps. 
I'm used a Dell OEM Win10 image that has been continually updated.  This last worked fine for 1703 image update, when I modified the image with Dell IA tools, is there any reason 1803 is different?  I'm using the current Dell IA tools 8.5.0.6.   Error message "Error: This is a retail version and is not supported by this tool" - It's not retail.  I'm not trying to blow 2+ days of configurations, setting, and a lot of research for a brand new image here and do it over again.  Any advice, please let me know.    
Retail version not supported by this tool