Not returning properties and/or categories in custom namespaces
It looks to me like this should be a very simple fix, if I'm reading things right...
First of all, you should switch to using defined constants instead of magic numbers:
## Define namespaces define( "NS_BLOG", 500 );
...as kgh recommended. Of course, you could just use the magic number 500 in both places, but it's better to use a defined constant to prevent mistakes.
Then register your namespace using the wikilog extension using your defined constant instead of the magic number "500":
Wikilog::setupNamespace(NS_BLOG, 'Blog', 'Blog_talk' );
...i.e., that's the same as writing
$wgExtraNamespaces[NS_BLOG] = "Blog"; to declare the new namespace, except it also does some additional setup related to the Wikilog extension, and ensures you declare the namespace correctly.
Now your namespace is set up, set it to allow semantic properties by adding
$smwgNamespacesWithSemanticLinks[NS_BLOG] = true;
...hope that helps.
I tried a large number of things until I figured out that I was making my smwgNamespacesWithSemanticLinks declarations *before* the enableSemantics call. When I moved them after it (as described in the documentation, although only briefly), everything started working great.