First, I am speaking from ignorance, but experienced ignorance!
But in my limited experience, there is no need for CalDigit firmware. I know that CalDigit used to insist on CalDigit-vetted drives, but I suspect that was more a matter of their selecting and testing the drives than anything else.
My HDOne started with all CalDigit-supplied drives. As they have failed (three of them), I sent them to Seagate for replacement under warranty. I put the replacement drives from Seagate into the HDOne as-is, without any firmware upgrades. They have worked fine.
When I started thinking about doubling the storage by replacing my 1TB with 2TB drives, I called CalDigit, bec. their website indicated that they were temporarily not able to supply the drives. So I asked what I could do. They were more open this time. My sense from talking with some CalDigit folks is that I will be fine with replacement drives, as long as they are no larger than 2TB. From reading online, I discovered that certain drives are listed as being especially appropriate for RAIDs.
Good luck.
Bob C