The whole sd-card or single partition usage is not possible on MinimigV1 board.
Since ARM require a FAT(16/32) formattet partition with the FPGA core file and Kickstart image, the sd-card or 1st partition must stay this way.
Yes, the first partition (or entire card, if unpartitioned) must remain FAT formatted. That goes for the TG68-based Minimig variants too.
If the card is partitioned, then it should be fine to use any but the first partition.
To make Amiga access a whole fat sd-card it may work in Workbench using CrossDOS. But in this case I doubt a 32GiB HC card will be accessable.
Not with CrossDOS, but Fat95 should be able to manage it. There are geometry problems that make using Fat95 hit and miss at the moment - I haven't had time to address them yet - but Fat95 is the intended use case for the whole card mode.
For instance, on my 16GB card, I have a 1 gig FAT partition, then a 4 GB partition containing an image of the hard drive from my old A4000/030. I have "Card Partition 2" as the primary hard drive, and "Entire Card" as the secondary hard drive, so I can mount the FAT partition using Fat95 for easy transfer of files.
In theory it should be possible to use Boot95 to put an RDB with the Fat95 filesystem on an SD card, and boot the Amiga from FAT, but I haven't managed to get that working yet.