I apologize for the lateness of my reply...
ISPF provides a workstation agent (WSA). You have to download it, install it, start it. It is a workstation program that ISPF can communicate with.
Your rexx program can run on TSO ISPF and can issue a workstation command like this:
/* rexx */
ip = 'xx.xx.144.175'
title = 'PEDRO'
/* connect to the workstation */
"wscon ip(ip) title(title) codepage(1140) " ||,
"charset(0695) noguidsp panel(onerror)"
/* launch the browser */
"select wscmd(C:\test\index.html) modeless min invis"
I am not familiar with VBA, but guess that if it has a line command interface, that you can indeed launch it from ISPF.