I am far from an authoritarian source, but in my opinion I don't see a moral problem. A prenuptial agreement doesn't encourage people to get a divorce in my opinion. It simply protects both parties assets that the had before the marriage should the marriage end in divorce.  
 
A prenuptial agreement is kinda like an insurance policy, it protects both parties in case the unspeakable happens. I don't know what the Church's official stance is on the issue and lds.org has nothing at all on prenuptial agreements so I am assuming the Church has no position for or against pre-nups. 
 
If I had anything of value before I got married that would of made getting a pre-nup worth the cost I definitely would of gotten one.  
 
In reality needing a pre-nup is silly in my opinion, you shouldn't need an agreement to know that whatever each party has before the marriage is theirs after the marriage, and all assets gained jointly in the marriage is to be divided 50/50. 
 
Without a pre-nup you can lose everything you worked hard for before you were married. Getting an agreement to protect that should the marriage dissolve is not a bad thing in my opinion.  
 
Everyone says that if they should get divorced they would be civil but most times what is said before a divorce and what happens during a divorce is two different things.  
 
If you have significant personal assets when you are preparing to get married you should prayerfully consider a prenuptial agreement even though divorce rates for couples sealed in the temple are low.