If they have a bitcoin wallet, then why not give them some of your bitcoin? it is not bad to give some of it and I think newly weds will also appreciate your gift because you still give effort to give a gift to them and if they already know about bitcoin and they also have bitcoin, for sure they will really love your give and save it for their budget for their honeymoon. 
It is a nice idea to gift the wedding couple a bitcoin,if they have good awareness and knowledge of how to use the bitcoin in a right way,to make progress and to have financial growth.