Such words are fine, because it can be supposed that they are in fact borrowed in their plural form directly, such as data and literati (even when the singular exists with a slightly or largely different sense.) This is in principle the same as emprunting a verb form and using it as a noun (ignoramus, exit) or any such cross-functional usage.
Is there a strong difference in the use of "data" as plural between the American and British English? I say this because of the treatment of "parliament" as plural in British English, whereas Americans treat it as singular. To me, an American, I tend to think of "data" not as a number of individual facts, but as a collection of facts, and thus singular. On the other hand, I do us "datum" to mean "a piece of data," but I think that I am in the minority.