Fortunately, I found some other family documents from the 1900-1901 time frame which helped me verify that THIS family in the 1900 census IS my Belan family. As mentioned above, Rudolph Bellan was born in 1900, and George and Ursula had another baby, Olga, in 1901. I was able to find the Birth Returns for both of these children. In Cleveland, during this period, birth returns were simple forms that were submitted to the Secretary of the Public Health Division by the attending doctor or midwife. The birth return lists the date of birth, sex and race of child, place of birth, and names and ages of parents.
If you look carefully back at the 1900 census form above, you'll see that Ursula ('Mary') cannot speak English. (Understandable, since she's only been in the country about a year and a half.) I suspect that she may have gone by an 'easy' generic name in these first years after coming to America, as many immigrants tended to do. George and Ursula's next child, George, was born in 1903, and Ursula is indeed listed by her correct first name on that birth return.