Can Catholic actors accept roles that require of them nudity and enacting illicit sexual union on screen or stage?

As a general rule, no. To do this is to engage in scandal wherein one gives temptation to others, and contributes the lowering of moral standards. It is wrong to celebrate or encourage immoral activities. There is, however, the fact that movies and drama do comment on life and the human condition, which includes violence, treachery, corruption and sexual sins and so forth. To treat of these matters in drama, (as even the Bible does), is not per se wrong. What is wrong is to celebrate such sinfulness, or seek to justify and normalize it. 
 
Even more erroneous is to unnecessarily display what should not be seen. For example, to include a murder in a movie does not require us to watch a person brutally killed and dismembered. Likewise, to report a sexual infidelity does require us to watch it pornographically portrayed. Subtlety and discretion are required to treat topics like these. 
 
So Catholic actors should not transgress when sin is either celebrated or inappropriately displayed.