So a brief update to the second part of my query, after attending the Steelers game vs the Nottingham Panthers (the yellow jersey photo above) tonight, I can confirm that the outline colour is stitched onto the number, and then the whole thing is stitched onto the jersey. I'm almost certain that it's just a simple wide satin stitch that's used for the outline, and since the white Cardiff jersey has the same manufacturer, I suspect it's exactly the same technique. The material stumps me though. It's definitely not the kind of sports twill with adhesive on the back that they use in the NHL and, as said by Mike, there is in fact no glue or anything holding the numbers to the material.
So really, all i'm wondering now is: what kind of twill is used, if not the sports kind used in the NHL?