Em 2009, a IBM disse que não é compatível com o IE8. Não tenho certeza se isso foi corrigido, mas foi o que encontrei no site deles:
Support for Microsoft Internet Explorer 8 in WebSphere Host On-Demand Version 10
Technote (FAQ)
Question
- Does IBM WebSphere Host On-Demand Version 10 support using Microsoft Internet Explorer 8?
Answer
- Currently Host On-Demand Version 10 does not support Microsoft Internet Explorer 8. The development team is investigating the support for Internet Explorer 8 with Host On-Demand. During the download, the progress bar does not display and no download takes place. This has been tested with different levels of Java and the cached client will not install. The Download clients and Webstart clients are not affected and will load. Development is targeting fourth quarter of 2009 to have a resolution to this problem.
O site Página do WebSphere Host on Demand da IBM detalha mais sobre os requisitos.