tribe_in_category

/**
 * Tests to see if the current event is assigned to the specified category or
 * categories.
 *
 * @param $ids int|array
 * @return bool
 */
function tribe_in_category( $ids ) {
    $ids = (array) $ids;
    $categories = get_the_terms( get_the_ID(), TribeEvents::TAXONOMY );

    foreach ( $categories as $category )
        if ( in_array( $category->term_id, $ids ) )
            return true;

    return false;
}

// Conditional test that could be included in ecp-single-template.php
if ( tribe_in_category( 4 ) ) echo 'Go category 4! Yeah!';
else echo 'This category is for losers!';