If you mean redundancy as in multiple whistles, yes, that's a good idea. On my hiking backpacks I attached a whistle on each of the main zippers. Why not? It is light, inexpensive and serves a practical purpose.

If you want inexpensive redundancy, then I recommend these fake Fox 40 whistles that are just as loud as the real thing:
http://www.amazon.com/Price-10-Pieces-Pe...4448&sr=8-2

(Do an Internet to find an even lower price elsewhere.)