@bigdogdch Yep sure can. The creatures with changeling (or spells with changeling) don't need to be on the battlefield for that effect. They are all creature types regardless of which zone they are in.
Neat deck idea, if it were me though (depending on your playgroup), I'd
consider swapping out several of your non-gate lands for basic lands.
Blood Moon or another similar type effect is going to be REAL tough on you, and take away your win-con. If you're really worried about mana-fixing,
Chromatic Lantern effects are the way to go, not multi-colored lands that enter tapped, IMO.
Cool stuff though, +1 from me