Nope. Once Apple stops signing firmware, you can't save them.
I would imagine that if he were to use that option in Cydia, the only SHSH blobs that would be saved would be 4.3 (and/or 4.3.1).
When you have Cydia saving SHSH blobs, what it actually does that first time is talk with Apple computers to get the authorization key. Then, it's taking that response from Apple and saving it somehow on their servers. That is all it does - and only that first time. It'll never talk to Apple about that version again.
Then later, when you ask for an authorization key for that firmware (in this case, 4.2.1), that request is not going to Apple, it's going to the Cydia server that acts like Apple (that saved your blobs initially). So, since it saved the response from the first time (when Apple said "yes, it's good"), it sends a good-to-go response to iTunes that it's an okay firmware version. IOW, it's fooling iTunes into thinking it's talking to Apple's servers, when really it's talking to Cydia's.
If you don't save the SHSH blobs on Cydia (with/without Tiny Umbrella), before Apple stops signing [approving] them, then when iTunes asks for authorization/verification - it's going straight to Apple. Their servers will deny the authorization because Apple has stopped signing it.
So, long story longer: So, if you have iOS 4.2.1 and if you've never saved your SHSH blobs and you try to save your SHSH blobs, that initial request, even if going through Cydia/Tiny Umbrella, goes straight to Apple, just like normal. However, Apple's computers will deny that request.
There, now that's clear as mud and probably way more than you care to hear. I just found all this stuff fascinating while I was researching as to whether to jailbreak or not. Though I understand what's going on, I can't do any of this technical stuff and am way impressed with the programmers of jailbreak asssets.
Anyway. Sorry to ramble and hope it answered your question.
Marilyn