Can anyone think of a reason for an ogre or troll SK to go 1h + shield
 

I intend to go for it on my alt, even though it seems to make more sense to just use 2h + slam. But is there some valid reason for 1h + shield, like a particular weapon I may be unaware of, or a particularly useful secondary slot item that isn't a shield?

tanking

Shields do not get affected by the AC softcap, so they are good when tanking for a bit of extra mitigation. Also, SKs do get some good 1h weapons like Ebon Mace. Its one of the better weapons you can get if you are on a budget. Obviously something like Reaver is way better if you can afford it for leveling, but it is much more expensive comparatively, and not always easy to resell.

More stats on a 1h + shield. Also if you're on Green, 2h suffer a bit until the October 2001 patch. I'm a troll using sword/board, but will likely use the 2h a lot more once the Oct. patch comes through.

Just use the best weapon you can get imho.

Out of curiosity, what kind of damage mitigation during fight would a 40 AC shield provide over the course of a fight with an even con mob?

My 52 troll sk uses the velks sword with clicky grim aura and shield or a reaver. It covers bases sufficiently well.