I really think it should be encouraged. The large number of famous artists that painted nudes hired prostitutes for the purpose.
A woman in her 'natural' nude state, after she's just fucked or just before, which is when her naked body is viewed, is in a certain state of physical abandon. A civvie is not very geared to doing that as an artist's model. Hence one sees a spate of asinine, sexless nudes.
There is every reason for an art student to study the naked body as it is the only real way to understand things like muscle tone and the articulation of the limbs (which somehow have to be suggested even when painting a clothed human figure): but for depicting a nude as a nude a prostitute is superior in my opinion.