Had to do a bit of research.....
First, what are the wiring installation requirements with respect to the cameras/system/kit you are using? Wire gauge, insulation, lengths/limits...?
Second, how is power being handled?
For example look at this device and its installation diagram:
http://www.cctvcamerapros.com/4-Channel-Video-Transmitter-p/balun-4phub.htm
Seems rather straightforward but not sure how directly applicable the design may be for your situation.
However, if you do an internet search for something along the lines of "home security camera wiring diagrams" you get diagrams such as these:
http://www.bing.com/images/search?q=home+security+camera+wiring+diagrams&qpvt=http%3a%2f%2fhome+security+camera+wiring+diagrams%2f&qpvt=http%3a%2f%2fhome+security+camera+wiring+diagrams%2f&qpvt=http%3a%2f%2fhome+security+camera+wiring+diagrams%2f&FORM=IGRE
Several of the diagrams/photographs etc. seem to be applicable. What that tells me is that what you have in mind is viable but the devil is in the details.
If you can diagram out your wiring plan with all connections, connectors, power, etc. then you may be good to go. Just be sure that all of the cabling/connectors, etc. meet the necessary specifications for outdoor use. Especially any specifications required by the cameras. May end up that a "camera failure" may not be covered by warranty if you did not adhere to the installation requirements.
Keep things simple and straight forward even if you have to run two lengths of Cat 5. Any cuts, splices, etc. may require repair which may not be fun if it is cold and wet out. Or hot, humid, buggy. Maybe standing on a ladder. Every connection is a potential point of failure. Does not take much to short out or cause break a connection somewhere....