Can, but can use those provided by Lenovo itself only.

In Y500 already have SSD Slot in the laptop no need to put the SSD in Ultra Bay

You can buy the mSATA SSD and insert in mSATA slot. Else you can buy normal SSD and swap with HDD, get Lenovo HDD ultrabay for HDD but quite costly. Its cheaper to use it as external HDD.

Beware the normal HDD caddy bay can not fit in the Y400/Y500 due to its design and ports.

The ultrabay optional accessories are not available in the local market currently. Wonder they will bring in the ultrabay accessories. 

You can refer to ultrabay accessories selling at US Lenovo for more details.
http://shop.lenovo.com/SEUILibrary/control...e&cc=us&lang=en

Here the pics for ultrabay accessories.

This is where they make their money lol. 

Y500 with dual gpus(gt650m SLI) is overkill since you are not into gaming.
Latest Y500 bundle with both 120w & 170w psu. You can bring the 120w psu when you need mobility. Swap in the ultrabay gpu and use 170w psu when you need the extra gpu performance.

If you want i7 , full HD laptop and don't mind the overkill gtx660m. Better get the cheaper Y580@2999 with gtx660m and longer battery life. Use the remaining budget to buy SSD and swap it with HDD, get a much cheaper HDD caddy bay and swap it with ODD. use the ODD as external drive. If you wish to retain the ODD,  then get the mSATA SSD for mSATA slot.