you are confused.
each firmware version will have different ecid/shsh blob.
The ecid is unique for each device.
for fw 3.0 - you have a shsh blob for that
for fw 3.1 - you have a shsh blob for that
Getting a 3.0 shsh is no longer possible because Apple does not sign that fw anymore. For those who have 3.0 shsh blob, they are lucky because Saurik enable that service right before apple stopped sigining 3.0
If you have 3.0 shsh on Saurik's, you will see it in Cydia. If not, you don't have it and you cannot restore using 3.0 fw.
If you have 3.0 shsh on Saurik's server, you can retrieve it to your computer using umbrella.
At the moment, you can get fw 3.1 shsh blob for your device via cydia or umbrella. This does not require you to be running fw 3.1 on the phone.
This 3.1 shsh blob is for safeguarding .... You cannot use it to restore your phone 3.0.