The reason that Saruman the White Hand cannot use the Spells of Dismay, is because he is not Saruman the White. They are two separate profiles that represent Saruman at different times during the War of the Ring.
I.E - Saruman the White is when he is a member of the White Council, before he openly begins searching for the One Ring. He has already secretly started though, hence the Spells of Dismay.
Saruman the White Hand is after his true intentions have been revealed. Consider that at this point, he has his Uruk-hai army, and is openly waging war, rather than using his previous attempts at subterfuge.
I don't agree with that line of thought in regards to what spells he should have lost/kept during that transition.
I think it stands to reason that GW made a typo, writing Command instead of Dismay on Saruman the White Hand, because:
1) Gandalf and Radagast, along with plenty of elves (Galadriel, Celeborn, Elrond and Cirdan), knows all the Spells of Command.
Saruman the White was a wizard of good faction and knew all the Spells of Command (along with Dismay and Ruin)
No evil wizards know any Spells of Command (apart from Saruman).
2) Plenty of evil wizards know Spells of Dismay, Sauron and Ringwraiths among others, and it doesn't get any more evil than those...
Only 3 good faction wizards know them, and Saruman the White being one (Gandalf and Galadriel the others, although I may have missed someone)
Going from Good to Evil, why would Saruman not loose the "Good" spells of Command instead of the "Evil" spells of Dismay. I can't really see him using magic such as "Blessing of the Valar" or "Instil Valour", let alone have them instead of "Visions of Woe" or "Terrifying Aura".
I mean I'd love to be able to bring back Berserkers with "Blessing of the Valar", but it just doesn't feel right.
In the SBG, as far as I can tell, he seems a lot closer to Dismay (with Terrifying Aura + Transfix (basically the same Immobolise as in the SBG, not the watered down version in spells of Command)).
Imo we should all be playing with Saruman the White Hand as Ruin+Dismay.