Cool looking rack. Something to consider is how you are going to stain or paint the antlers? I would agree with you on the epoxy sculpt, if fills in better and is stronger. However, the problem with the epoxy sculpt or magic smooth, similar two-part epoxies, is they don't hold a stain. They hold paint okay, but when you try and stain the antlers you will see a great difference of color between the actual antler and where the epoxy sculpt is. When I do a antler tine replacement/repair I will use the epoxy sculpt due to the structural integrity and easy to mold, however for what you are doing, which is just to fill small cracks I would choose something differently.
For what you are trying to do, I would honestly use a light colored wood filler by watering it down slightly to make an easy fill into the small cracks. The wood filler will take stain in the same consistency as the weathered antler and will look better.
Stain is a biggie too..wouldn't use a regular wood stain as no matter how 'flat' the stain claims to be it comes off making the antler have a wet look. I would only use paint as a LAST resort to getting color to antlers. Commercial antler stain works great, but only for 1 or 2 coats at the most and then it does the same thing. For those antlers, especially being weathered, I would do a coffee stain. Get a small can of the darkest roast coffee you can find. Wear gloves and do this over some cardboard or an area you don't care about getting some color on. Mix the grinds with just enough HOT water to make a paste. Liberally rub the antlers down with the paste and let them antlers sit with the grinds on them for at least 30 minutes. Brush off and do it again if you want a darker look. Its a great way to stain weathered antlers, gives a more natural finish, and ends up smelling great too, lol. When you get the color level you want, just used a brush to remove any excess and wipe the antlers down with a light coat of MinWax 'Light' or 'Medium' Walnut floor wax on a paper towel. This will seal them and enhance the color slightly.
Give me a call if you have any questions and best of luck!
Joel-BRT