I am able to see the Saab forum. I didn't register / login, so no attempt to post anything, but it appears the same as what I see on a PC, including images.
This is on a TP with the stock webOS browser.
Checking on a Pre3, at first it appeared to load, but I got a white screen. I reloaded and saw the site banner, which then vanished. The same thing happened on a second reload. To me, this suggests some script the browser doesn't like. A trick I sometimes use is to stop the load when the content appears, but before the scripts do (theres often a pause near the end of the process when all the 'fat' of the page - Ads, videos etc - are being downloaded). Doing this retains the banners and background image, but no content - I think these forums are 'generated' anyway - no fixed HTML content. That said, I can view and post on this (here) site with the phone & tablet browsers.
I am using a hosts file that blocks some sites (including some ad sites: Blocking Unwanted Connections with a Hosts File), but I think I've got that on all devices.
So, there appears to be an issue, but not for me on the tablet.
Have you tried Grabber5.0's forums app?