Nobody knows that, because Wałęsa never talked about Kosovo.
Then, he is wise. He is aware of importance of that question for international relations, for the Serbs and that way for Poles. So, he won`t lure himself easely in discussion on that matter. No doubts that he knows history and knows a lot of about Serbs, about Balkan, about.... If he didn`t support Tusk on Kosovo then, Tusk is already pollitical oblivion. Probably, Polish inteligentsia keeping some cards for the last moment and Walesa could be that card or aware that card must exist and must be played, sooner or later.
No doubt, if Walesa didn`t publicly support Kosovo separation (recognition by Tusk), Walesa most probably support Serbs, meaning... Walesa probably belong to progressive Polish inteligentsia that hold to Polish national and specific interests.