Short answer, no you don’t need ISRC codes. If you don’t have any just leave that column blank and burn the CD. ISRC codes allow tracks to be monitored when played by radio or TV or in other public forums. They’re used primarily for sorting out royalty payments. If you don’t have ISRC codes for the tracks that are making up your CD then don’t worry about it.
AFAIK, and someone correct me if I’m wrong, but right now in 2015 almost every audio CD you buy or create conforms to the Redbook standard. The Redbook CD standard is a set of technical specifications that allow all the audio and accompanying information you might find to on a CD to be on there in a predictable, standardised way. It makes writing and reading CDs easier for manufacturers of CDs and playback systems (and mastering engineers!). The info you would find on a Redbook format CD includes the audio, the track start/stop information, CD Text, ISRC codes, the barcode and other bits and pieces. AFAIK the only information needed to create a Redbook format CD is the audio and track start/stop info. The other stuff is optional. Wavelab allows you to add this extra info as CD authoring is a big part of what it does.