The fact is that all the other encounters went the other way round, with a Germanic speaking conquering layer dominating a much larger Romance populace, but acknowledging the cultural dominance of Latin.
It is of course possible that a part of Germany (in the broadest sense) comes to be dominated by Romance-speaking rulers (well, in a sense it happened in modern times in Belgium for a while, and in Alsace-Lorraine, but I have no clue of whether that influenced the local spoken forms towards hybridization; the conditions were WAY different with the Anglo-Saxon/Anglo-Norman situation).
On the Romance side, I suppose that can be argued that Ladin spoken in the Italian and Swiss Alps can be considered an hybrid to some extent.
However, I'd suggest another scenario:
The inner parts of southern Appenines saw massive Langobardian settlement.
Langobardian is thought to have survived there for a good while, probably until the Norman Conquest, but the speakers where no so numerous. Finally, the Longobards and other groups they had absorbed (Bulgarians and possibly some Serbians) assimilated linguistically into the Romance-speaking majority.
If this does not happen (possible PODs are, more Longobards settled in the area, heavier toll of the Justinian plague depopulating it prior the Langobardian invasion, more local prestige for the germanic form, more numerous Bulgarian settlement with its subsequent linguistic germanization, etc.) you may have an heavily Romanicized Germanic language still in use over a large, albeit not densely populated, swathe of Southern Italy by when the Normans arrive. The Norman impact should be roughly similar to the one they had over Anglo-Saxon - Indeed, such "Southern Langobardian" spoken today, would someway resemble English, probably more the OTL German or Dutch do.