I'm building a Aeroworks 540t 60/90. I have the following for servos: 2-HS 225BB for the elev., 1-HS 625 MG for the rud., 1-JR NES 507 for the thro. and 2 - HS 5475HB (Digital) for the aileron (one in each wing).
What battery setup should I use?
Is it OK that I use digital and non digital at the same time?
I was thinking of using 2 -1100 NiCad with a y harness, will this be O.K?

first of all, i would not use 225s for the tail. use standard servos whenever possible. standard servos are much more robust, and you can not afford having something go wrong on the tail. it if ends up being too tailheavy, or you believe it will, being the servos inside and use a pull-pull. but then again, that is jsut what i would do. 2nd. you can run any combination of servos you like, digital or non digital. however, 2 1100 mah nicads are way overkill and will just add to the weight of the already heavy edge. you want to keep that plane as light as possible, because heavy aerobatic planes express bad habbits at low speeds or high AOA. digitals draw a lot more current than normal servos, and so far i get about 5-6 flights of my 2100 metal hydride batteries, and i am flying 3d, with 5 digitals. i would recomend only 1 1100 mah nicad.

So long as you use one switch for each battery pack then yes, this will work.

it will work, but that's just another 6 oz or so.