Drupal - Is there a way to set block visibility programmatically without using the PHP Filter module?

Yes. Setting the blocks content to false will hide it from the display and will hide the region if there are no other blocks present. I'd imagine you would need a setup similar to the following:

$block['content'] = _my_module_custom_block();

...

function _my_module_custom_block(){
    if( HIDE_CONDITION )
        return false;
}