Every BizTalk solution should have some kind of monitoring in place. I remember the phrase having a BizTalk environment without monitoring in place is like driving a car without a dashboard. The best option will be to use SCOM (Microsoft System Centre operation manager) to monitor BizTalk server, since you will get out of the box SCOM packages with prebuilt rules and alerts to get you started.
But sooner or later you?ll face the reality, big enterprises will have some kind of monitoring solution in place (in this case HP OpenView) and they won?t be interested in getting a new product into their arsenal. There is nothing wrong with this, new product will introduce new complexities, it won?t fit with the process/workflow they have defined already for monitoring and alerting etc, etc.
We were hit with the exact same issue and Michael Stephenson a fellow BizTalk server MVP came with the idea of putting a white paper explaining how they used HP Openview to monitor a BizTalk implementation, I was in a similar situation, written an internal document for my current client. So we merged the ideas and came out with a white paper which can be downloaded from the following link http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=b66856e0-81a2-4969-b6f7-1abb990a67db
Hope its useful.