It would suck anyway. I don't know if the iCade and else supports these, but if you don't have such 3rd party controller you're gonna be stuck with HUD controllers... which suck IMHO (starting from the fact PSx games weren't supposed to be played without a controller, so you will be covering the screen with your fingers all the time).
Maybe Apple will release some controller in the future ($1 million dollar for the basic version, $1.5 for the version with more than two buttons), but for the time being if you are interested in emulation on-the-go, your best bet is Android, since it supports USB controllers out of the box.
However, I'd wait a little longer (end of this year) so you'd have choices with the new CPUs that are coming, that should run everything PSx and N64 full speed.
Now, I ain't trolling, just giving you options in case you are interested, no offense intended.