A shaman memorizes and casts spells from the Cleric Spell List (see table II.3.) and Magician Spell List (see table II.2.). Optionally, he may memorize and cast druid spells in place of cleric spells, and/or necromancer spells in place of magician spells, these drawn from the Druid Spell List (see table II.4.) and Necromancer Spell List (see table II.6.), respectively. The decision to practice a particular school of sorcery must be made at character creation and cannot later be reversed. Cleric (or druid) spells are granted by spirits of the dead.
ASSH Players' Manual, p. 62 wrote:
At 3rd level, a shaman of Good or Neutral alignment can exert control over the undead and some dæmonic beings, causing them to flee and/or cower. Evil shamans covet the submission and service of these foul creatures. In either case, the shaman must stand before the undead and boldly speak the commandments of his faith, displaying his totem symbol whilst doing so.
Shamans who use the druid spell list--can they still turn undead at 3rd level? I'm inclined to think so since both druid and cleric spells "are granted by spirits of the dead," not through the auspices of a god.
I consider the spellcasting and turning to be entirely separate abilities, so yes. Note that the necromancer can also turn (command) undead without being able to cast clerical spells.
Turning Undead is not a spell. Sorcery and Turn Undead are separate class abilities. Nothing indicates that changing the spell list would affect Turn Undead.
"Steel isn't strong, boy. Flesh is stronger. What is steel compared to the hand that wields it?"
ASSH Players' Manual, p. 61 wrote: