Botulism risk with refrigerated items
Botulism thrives in high-moisture, low-acidity, low-salinity, anaerobic environments at between 50 and 130 degrees. 

In your refridgerator pickles, you're:


keeping cold 
adding acid 
adding salt


All of which should at least prevent the botulism from reproducing in great enough numbers to be toxic, if not outright killing it.

That's not to say nothing nasty can grow in refrigerator pickles &mdash; you're likely safe from botulism, however.