OK to use both yum and rpm on same system?

[Ted]

Hi, I'm new to Linux and currently using rpm with FC1.  My questions are 
about using both yum and rpm for package management on a single system:

1. If I use yum to install package X, will rpm recognize package X is 
now installed?

2. Will rpm be able to update package X that was installed by yum?

3. Is it bad practice to mix yum and rpm for package management on my 
system?  In other words, if I begin using yum, does that mean I should 
stop using rpm?

Many thanks,
Ted.