Well, the Wends did attack the Saxons and vice versa all the time, so no doubt they'll keep doing that. The question is, will their newfound Christianity matter? IMO the first question will be who Christianises the Wends, and how. If they become orthodox, they will most likely simply go on with their border raids as they had, and frequently get the worst of it, Jesus or no Jesus. If they go Catholic, though, they will have links to the Carolingian empire that is just now developing the concept of conversion by the sword. in that case, they are likely to participate in the Saxon Wars as they did IOTL, though more so.
That is, of course, a ceteris paribus assumption that is very hard to sustain. If there still is a Carolingian empire and Bonifatian mission and there is a Donation of Pepin and an independent papacy, then what changed to make the Wends, of all people, Catholic without altering anything else? I can't quite see it.