Is it possible to have 2 publishing rules on ISA, i.e; for EAS & OWA with same web listeners, same IP & port, & the same URL (email.abc.com) having a different authentication method?

Hi,

Technically no.

However, if you configure a listener for Forms Based Auth you can have your OWA users authenticate using forms and ActiveSync users using basic auth. This is possible since FBA will "fall back" to basic auth when it detects a user agent not capable of FBA such as an ActiveSync client.