Both songs do sample from a similar source: 50 Cent's sample is from a song by the Trammps called Rubber Band, and the Christina Milian song uses Jackie Moore's Clean Up Your Own Yard. Both are R&B songs from the early 70s, which is why they share a similar groove - so, if you want to call it something, early 70s R&B should be a sufficient description. Or, reference the songs in particular.
In terms of rhythms and basslines that do have names independent of a genre, these are usually limited to the very basics, like a walking bassline, or a swung rhythm, or even a polyrhythm. As you can see, these are a part of musical theory that can be applied in just about any genre.