If I import my private key is this just going to create a watch feature in the Electrum wallet to confirm there are funds at the corresponding bitcoin address?
Yes.
Which I can then check against the Bitcoin address with the funds on my blockchain.com account to confirm they match?
Yes.
I just don't want to sweep the BTC from my blockchain.com account and then not have access to the funds at the new Electrum wallet if it gets deleted when rebooting tails.
You're not even give Tails internet access. So it can't sweep anything.