I am looking for a Bitcoin HD Wallet which either allows to import existing vanity addresses
These two things are essentially mutually exclusive... you cannot import private keys into an HD wallet. The whole point of an HD wallet is that all the addresses in it are derived from the seed.
or which itself allows to generate vanity addresses by means of particular patterns?
This is theoretically possible... but because the wallet would have to start generating addresses from the seed to try and match the desired "vanity" tag, the search space becomes limited and the time required to find a matching addresses would be increased. Most likely rendering the entire process very lengthy and uneconomic.
Given that a vanity tags longer than 6 characters take hours/days of searching to find... and then you restrict the search to a specific sequence of addresses being generated... you're going to be crunching addresses for quite a while trying to find what you want.