Only in that it involves mergers. Eliss uses direct-control rather than movement, allows splitting, and the goals are different (you don't need to conquer the whole field, but to fill a specific number of traps). Furthermore sizes are irrelevant to mergeability, only color is important.

Osmos has a much slower and more reflexive gameplay, Eliss is faster-paced and reactive. At the end of the day, they're very different games although both fall under an umbrella of "extended puzzle games" I guess.