Let's see...
Using
Skippy my Druid/Shifter/Monk from Ziroc's Escape from Undermountain mod:
With no items on him AC=28 and he has full monk unarmed attack progression (5 attacks/round); shifted into Red Dragon shape AC=61 with full monk unarmed attack progression.
With +1 hide armour on him AC=22 and he has normal Druid attack progression (3 attacks/round); shifted into Red Dragon shape AC=62 with full monk unarmed attack progression.
With no armour and Hammerfell's Dwarven Shield of Protection +3 on him AC=22 and he has normal Druid attack progression (3 attacks/round); shifted into Red Dragon shape AC=64 with full monk unarmed attack progression.
So your armour merges with the "hide" of your shape and passes along whatever "+" bonus as well.