I don't understand why people don't think this is possible.
Lets think about the facts for a moment.
Its a TV show.
Its written by people.
Anything is possible in the realms of imagination.
Now, if we take those on board and re-write Angel Season 2/3/4/5 to not involve the creation of Connor but everything else, more or less, happens as is, could Groo have fathered Jasmine in season 4 in 'Apocalypse Nowish(?)' by having sexual relations with possessed Cordelia, remembering that he himself is not a Human, instead a 'Half Breed'?....ummmm yes.
Would it be believeable?.....ummmm yes.
Infact taking into account the 'facts' I used up at the top, would it have been possible for the father to have been Fred using a strap-on and Burger King special Sauce?.....ummm yes(and kinda the one I want to see).
If anyone is suggesting that Groo is the Father of Jasmine now, then thats a separate issue, as we know that he isn't, but if the question is 'is it possible?' tyhen absolutely.