You're probably best off using the serialization and deserialization from rosserial, even if you don't use the rest of it.
You probably just need msg.h ( https://github.com/ros-drivers/rosser... ) and the generated message classes from make_libraries.py . If you have a small set of messages you probably don't need to use the full rosserial build system; you can just generate messages once and then check in the resulting headers and use them.
Pulling in the full serialization libraries from roscpp probably isn't a good idea. I think they depend on boost (which is going to be difficult to get on arduino) and they use 64-bit floating point, which isn't supported on arduino/AVR ( as noted in the rosserial msg.h above). There are probably other dependencies in there as well that will be difficult to make work on an AVR.
You may want to dig into rosserial_arduino; I know it uses a serialiazation that is similar to the stock serialization, and I think it has a few modifications to make it more arduino-friendly.
It would also improve your question to explain WHY you want to do this; there's a decent chance that someone in the community has already done something similar and can save you a great deal of effort (see also: XY problem )
So, I have a server that is taking ShapeShifter messages and serializing them and then needs to send them to the Arduino, is this feasible, or should I be looking more into a custom serialization? I hvae looked some into rosserial and am lost in it.
I Edited the question to make it clear on the outcome
That sound almost exactly like what rosserial is doing (the C++ uses ShapeShifter too), and rosserial has some additional protocol over the serial line to delimit messages and identify which topics they belong to. you may want to read http://wiki.ros.org/rosserial/Overvie...
Overall it sounds like you're reinventing rosserial, and unless you've gotten rosserial to work and found it unsuitable, I'd advise that you give it another go.
There's been some progress in this question getting rosserial_arduino to work over the arduino wifi shield; you may be able to use that or adapt it for an ethernet shield.
The particular reason that I do not want to go with ROS serial is that future add-ons that I plan for the project would make it complex to handle within rosserial.