Possible, but unlikely.
MOTD url is separate of FastDL variable.
More likely, unless Gmod/Source code has changed in past few years re:HTML/motd...you can't load dynamic images, scripts, etc.
Heck, I can't even load that page you linked w/o Firefox telling me I need additional plugins.
For testing, try just a flat html "hello world" page.
Also, and this may have changed too, if using a listen server, don't think you can view even a remote http page connecting to yourself.
Been a long time since I've used/messed with any of the above, so please ignore any smoke coming out of my ears.