Can I safely substitute a 4.7uF cap for a 5uF cap?
Without knowing the details of the circuit, it is impossible to tell.  Specifically we don't know exactly how this cap will be used, and so we do not know how critical the value is or what tolerance is required.  

In many applications that substitution is acceptable, but in some it might not be.

But, wait, there is more!  5.0 uF is not a common value of cap.  In fact, I have NEVER seen a 5.0 uF cap.  I'm sure there is one out there, but it is probably some weird cap intended for some weird application with an equally weird price.  Basically, not something that 99.99% of the people will ever use in real life.  Even then, 5.1 uF cap would be a more likely value (because it is a more "standard number").

Here is a web page showing standard cap values:  http://www.rfcafe.com/references/electrical/capacitor-values.htm