The VIMM account is standalone, so if you login to it, and then connect a hive wallet via HiveSigner you'll be fine.
However, if steemconnect is your only way to login to your VIMM account, you'll be unable to login and using hivesigner will create a new standalone VIMM account. (Meaning you would lose your VIMM settings, your followers, etc...)
We'll give everyone some time to get that sorted out. But on May 1st, SteemConnect support will be disabled and those who don't have another login method setup will have to start from scratch with a new VIMM account. OR if their email is verified, we'll be able to send a temporary password so they can retrieve their account.
But the point remains, Easiest way to make sure you never lose access is this: Verify your email, set a VIMM password, and have more than 1 login method set up.