Employee
Nimbostratus
I see the SAP application owners pushing the SAP Web Dispatcher all the time and have found that while it does integrate nicely into the SAP solution you do lose the ability to offer some key components that you have with external load balancing. Since Web Dispatcher requires the message server to update the status of the portal services you will always have some delay and possible persistence issues that will need to be addressed with a re-authentication in a failure state.
Using the LTM we can also check the health of the servers as you pointed out in your post, and with the version 10.x of TMOS you can now turn on inband monitoring. The LTM will provide a high availability environment, and with iRules and iControl you can modify the traffic to meet you customers needs and manage the LTM.