Hi Sid,
I've heard that the subsitute for ice-cream - called Rice Dream - dose not taste good.
.............. I have copied over a post by someone whose son has a very bad problem with lactose:
".....my DS has a life-threatening anaphylactic allergy to milk, eggs and nuts. He also thinks Rice Dream tastes like the "bottom of the cesspool" (He's 15.) With some negotiating, we have been able to get the Epcot restaurants, including the Land, to supply Sorbet for his dessert, which he much prefers to Rice Dream. The last time, they went over to the Coral Reef to get some.
I would call ahead and insist on speaking to the chef........don't count on a substitute automatically being there without some extensive confirmation.
In a counterpoint to this, we had a PS at Bomas. There were no dessert there he could eat. The chef personally made him fresh sorbet and a wonderful deepfried mango pastry. It was the most magical meal we had".
With the sit down restaurants, they do try to be very accommodating to allergy sufferers - tell the restaurant when you make your PS and again when you check-in.