I've been bowling with a combination of Ebonite and Hammer (current and Fab) for nearly 30 years. I have had only the following balls crack on me within the past 3 months, all due to non-use:
Ebonite Apex Addiction: bought in 1999, last used in 2003.
Ebonite XXXcel: bought in 2005, last used in 2008.
Ebonite TPC Warrior: bought in 2002, last used in 2012.
Out of Hammer's line, I've thrown the following: Faball Blue, Faball Blue Pearl, 3D-Offset, First Blood, Cold Blood, True Blood, Cube, Absolut Curve, Absolut Flip, Deadly Aim, BW Legend, BW Red Legend, ALF Solid. None of those have cracked.
Out of EBI's line: Turbo/X, Nitro/R, Nitro/R2, Optyx Formula 1, Total NV, Complete NV, Mission, Mission Domination/250K, Challenge, Pursuit/S, and Pivot. Again, only the above 3 EBI balls have cracked.
I will caveat this by saying that those 3 EBI balls were pre-Hammer acquisition. But I haven't had any issues at all from balls cracking that weren't through extended periods of non-use.
BL.