Is it mandatory for vendor's representative to be present in during bid openning?

yes it is mandatory for win win management.

Bid package assessment are either close or open in todays more advance system most organisation make use of e-soursing tools for vendors quote assessments through specific lots which could be procurement,civil and constructions all the vendors are brought together via online management system the winning bid is achived through a define time based programm. However in some goverment or parastatals vendors are invited to create an ope field for everyone and the room for clear cut openes for easy assessment by every one to select the winning bid