Want to know if ICS can mount an SD when formatted as EXT4 or does it still need a FAT32 partition like Gingerbread. Googled for 30+ mins, can't find an answer.
Two separate issues.
In short, it's impossible to answer if "ICS" works with ext4. It might work, but force ext4 into vfat instantly. It might not work at all. What's important is that you check if the ROM you are using both supports ext4 and does not force it back to vfat. Only one way to find out, except asking around xda-developers ;)
ICS usually has Ext4 support. The Google Nexus S for example had that already with Gingerbread. It depends on your actual phone model however:
This gives you a list of supported file systems. Execute the above command using any terminal app, eg. "System Tuner pro" -> Terminal
You don't need any rooting to view what file system your android kernel supports. My ICS 4.0.4 shows ext4 support.
Older droids were vFat mostly.