If a company filed for Chapter 11 can a vendor still provide services on a cash before delivery terms

You can decide to continue to do business with a debtor in a Chapter 11 only on a cash basis. What you cannot do is try to collect money owed before the bankruptcy was filed (except through the bankruptcy court process).

In addition, post-petition transactions, such as the ones you contemplate, will receive a higher priority for payment than most other bills (especially, old bills).