There is nothing official or definitive regarding the relationship between Gantu and Worf.
Other than Gantu's mannerisms and disposition, the only connection I can detect is that, before Kevin Michael Richardson had voiced Captain Gantu in Lilo & Stitch (2002), he had also voiced Sarevok Anchev, Gorgeig, Cohrvale, and Yaga-Shura in the game Baldur's Gate II: Shadows of Amn (2000). Michael Dorn had lent his voice to Bhaal for the the same game — an uncredited but widely-known role. The time difference between the release of the game and the completion of any voice work for Lilo & Stitch was probably about a year.
Given that Dorn voiced Bhaal and Richardson voiced a Bhaalspawn in Shadows of Amn, there is a basis for them having spoken to one another about their roles. As Richardson was one of the primary voice actors associated with the early Baldur's Gate games, he could very well have been the one to bring Dorn into the Baldur's Gate fold. However, this is pure speculation, and the extent to which they have spoken to one another has not been commented upon. (They could just as easily have phoned in their lines from separate locations without ever meeting.) There is, nonetheless, a possibility that Dorn could have influenced Richardson's portrayal of Gantu via this channel, especially given the proximity in time to Richardson's work on Lilo & Stitch. At a more basic level, Richardson may have been a fan of Worf, causing him to both bring Dorn into Baldur's Gate and to portray Gantu in a Worf-like way.
Even with such considerations in mind, it is unclear how much liberty Richardson would have been given with his lines, apart from the way in which he chose to project them. But then again, given that the writer of the film (Chris Sanders) was also one of the voice actors — Stitch himself! — there may be been a measure of liberty for the voice actors to experiment within reason.
Or it could all be a coincidence.
Speculation aside, I can find no actual, concrete evidence that Gantu was based on Worf. If Gantu was indeed modelled on everyone's favourite Klingon, then no one associated to Lilo & Stitch has bothered to say so.