The generic proxy support is never supported as a frontend to WebSphere Application Server. The WebSphere Plugin is the only supported mechanism to connect IHS with WebSphere Application Server.
If your entitlement to IBM HTTP Server is via a WebSphere Application Server license, then IHS is licensed and supported only as a frontend to WebSphere Application Server.
Some very limited reverse proxy (gateway) usage in such an instance of IHS can be supported, but not in the following cases:
Forward proxy is not supported when IHS is provided with WebSphere Application Server, even in cases where a customer writes an application that requires a forward proxy and deploys it to WebSphere Application Server.
An example of a supported usage would be to forward small ranges of the URI-space to another server during a period of migration, or to workaround virtual-host related configuration issues.
If you're using the free web download of IHS, IHS is may be used in any manner without support.
Customers interested in support of IHS used as a generic proxy can obtain a standalone support agreement. This agreement does not permit using IHS as a frontend to non-IBM Java Application Servers, but carries no other significant restrictions. It is the customers responsibility to make sure IHS is fit for their needs, as IHS is not a full-features proxy server.
Finally, customers using Proxy functionality are encouraged to move to IHS 7.0 if possible.