It appears to be fairly common, yes. Have a look at the Wikipedia article on software versioning.
Quote below is from that page:
Designating development stage
Some schemes use a zero in the first sequence to designate alpha or beta status for releases that are not stable enough for general or practical deployment and are intended for testing or internal use only.
It can be used in the third position:
0 for alpha (status)
1 for beta (status)
2 for release candidate
3 for (final) release
188.8.131.52 instead of 1.2-a1
184.108.40.206 instead of 1.2-b2 (beta with some bug fixes)
220.127.116.11 instead of 1.2-rc3 (release candidate)
18.104.22.168 instead of 1.2-r (commercial distribution)
22.214.171.124 instead of 1.2-r5 (commercial distribution with many bug fixes)