Apply system Configuration with %serialnumber% should resolve the issue of hostname; if wmic output of SerialNumber and IdentityNumber are same for following commands (can run in Preboot/Production) for client where you want to use AssetTag:
1. x:\>wmic bios get name,serialnumber,version [Will give SerialNumber which is the Dell Service Tag]
2. x:\>wmic csproduct get name,vendor,identifyingNumber[Will give yet another service tag report]
AssetTag and Serial Number are mostly same here.
Existing supported tokens in DS 7.x are:
https://www-secure.symantec.com/connect/articles/tokens-deployment-solution-7x
Thanks.