Is 賖 just a variant of 賒？
賖 is listed in Hanyu Da Cidian and defined as:


  shē
  同“賒1”。


The entry for 賒 says:


  1 买物延期交款。




Zisea also just notes:


  同【赊】。 


Not sure if their info is from 字海 or 汉语大字典 but there is no mention of Chữ Nôm in either of the references. It seems to just be treated as a variant in modern Chinese.



Wiktionary also gives the following references:


  参考
  - 大字源：1673页，第14字
  - 汉语大字典：第6卷，3643页，第2字
  - 宋本广韵：165页，第3字
  - 辞海：1275页，第5行，第4字
  - Unihan数据：U+8CD6


and only mentions:


  异体字
   赊