Can silk touch shovels acquire all the same blocks silk touch pickaxes can?
No, you still need a pickaxe for ores.
From the wiki entry on silk touch (emphasis mine):
Allows the collection of normally unobtainable blocks such as Ores , Grass , Mycelium and Huge Mushrooms . A pickaxe must be used for stone-based blocks (ores), while any tool can harvest grass, mycelium, huge mushrooms...