Can a source code (including the libraries) written in LPC Xpresso be ported, preferably in an easy manner, to Keil uVision4 for ARM?
The answer is a little bit difficult.
An ide (uVision or EWARM or Code Red / eclipse) can have different compilers, particularly for an open source ide like eclipse: you can hang actually mdk or iar arm compilers now to eclipse.
IDE is simply an interface to integrate all little pieces together for better productivity.
Libraries are compiler-specific, as a result, not ide-aware.
So if the libraries in question are written for a compiler to be ported to, your code utilizing that library can be easily ported, short of your usual struggle with some syntax issues.
Now, most of the oem libraries on the arm are written for gcc, mdk and iar. The issue is likely cmsis: they may have been built on different versions of cmsis that your target platform may not support. In those cases, you can either sort it out or migrate with the host cmsis.