re: When's the last time a LSU pitcher was also in the hitting lineup?

Doesn't make sense risking an arm to run bases. If he's good enough to use on a regular basis, then he's good enough to not be worth the risk.

If he's a backup bullpen guy who is unlikely to see regular action, then sure you can DH him if it's your best option. Or move him into the lineup with the option to move him back into the bullpen if injuries or a lack of production require it.