No, they are completely separate. Meaning, even sending payments and getting change is to completely seperate addresses. So, only way to directly connect them (that I know of) is if you send between the two accounts in which case a wallet explorer can link them.
That won't really "link" the wallets. It will show that one address sent to another. But, there is no way to know the same person owns those addresses or that they came from the same seed.
It will link them.
If I send to you and you send to me, we are linked. I didn't say it was the same owner of both addresses. And, in this case, we have not proved that we can sign from each others coins.
Even if we both share signing from the same address doesn't mean we are the same person. Example: Several people were playing with a private key (redeemed casascius coin - and was even later made public). One of us would send a small amount and see who could sweep it first. Doing this a couple of times between the four of us ended up linking all 4 together (even a complete link since we could pull the funds out (sign from it)), but it doesn't mean we have access to each others coins. Using a walletexplorer though DID link the four of us together into a single wallet account. It was just an experiment proving that a walletexplorer / chainanalysis can be fooled.
