I think that maybe a blender animation (just based on the character and familiar mesh of the genitals), but I think both daz and blender use the same tricks. I can't think of any tutorials I have seen on this, so instead I will throw words at you and see what you are familiar with and what you would like to be further explained. The issue is that I use blender for everything and daz for character prototyping.
There are 4 things that could be happening, you only need 1 or 2 of them to fake the effect, but there isn't really true collision.
~ 1 morph or shape key can be used to open and close the orifice. Often in blender animation, a bone is scaled to open the orifice, where it actually is using its scale as a driving parameter to control other bones and shape keys to allow for very complex morphs and shapes. If you use this by itself, you basically have to hand animate the opening and closing to match the size of the object going in/out.
~ 2 Pull or push morph/shape-keys. To add another dimension of complexity to the animation, you can have these other shapes that deform the orifice to simulating something being pushed in or pulled out. Many daz genitals have these morphs ready, or there are many morph sets you can by for genitals that not only include different openings for different size objects, but also have these push pull morphs aswell that you can mix in. again at this point you would have to hand animate this effect in. and for the most part hand animation is the only way to add this effect unless you want to do some coding and math that does a bit of integration.
~ 3 Simulation. I don't know what daz does since I only use it for character prototyping, but you can have a very simple physics animation that does 1 of 2 things. 1 you can have a very basic collition check to see how large the object going in is, this can control how to open the orifice. In blender I just do tricks with rigid body and hinges to do this, but the quality is never as good as just doing it by hand. 2 In blender I know you can do a lower resolution mesh deform with a soft body simulation, this will not be very detailed or accurate, but it can add effects like volume preservation and add effects beyond what the 2 types of morphs can do, but you will still have to use the morphs to clean things up. I can get into further details on how to do this, but only with blender, I don't know if this is something daz can do or if there is a plug in or something for this.
~ Shrinkwrapping. again I am more familiar with blender than daz. Shrinkwrap can be a last bit of detail to make the private hug the inserted object, but it is very simple and requires you to use it with care, but everyone has a different philosophy on how to properly use it.
