I would be concerned about the difference in thermal conductivity and well as thermal expansion between the aluminum fixture and the steel hub. Hot hubs get backed into the water, the aluminum caps cool faster than the steel hubs, caps falls out!
An ordinary steel caps might work fine, and sure cost a lot less.
I pull a skeeter with aluminum wheels and hubs for hours. As soon as I stop for gas, or whatever, I feel them for heat. They don’t get hot enough for them to even be considered warm. I don’t think a few degrees is going to cause anywhere near the thermal expansion you’d need for a hub to distort enough for a cap to fall out. I have bearing buddies with the cap friction fitted to the hub and haven’t lost one in the 17 years they’ve been there.