In the US, "data" is treated as a singular noun, for example: The data for the report is ready. "Data" can also be considered a plural noun, but saying, "The data for the report are ready.", sounds overly-formal.
I'm one of those who treats "data" as singular, so I wouldn't expect "them" to feel right. However, for people who treat the word as plural, wouldn't "them" be the choice when an object pronoun was required?
As soon as the data was ready, I entered it onto the computer. As soon as the data were ready, I entered them onto the computer.