Although the E55 is just 1.5 years old, there are still 3 generations between it and Symbian^3, since S60 3rd FP2 is much older
Code:
Symbian 9.3 -- S60 3rd FP2
Symbian 9.4 -- S60 5th --- Symbian^1
-------------------------- Symbian^2
-------------------------- Symbian^3
Of course you can try all kinds of voodoos, installing code built with the Symbian^3 SDK, attempting to copy the missing libraries to the S60 3rd FP2 SDK. It will probably compile, just I would not expect that it is also going to work. But you can try, it will not hurt neither you, nor the phone.