I don't crimp rifle cartridges, but I also don't load for any semi-auto rifles.
I really don't see how it would be strictly necessary, as long as the sizer die sizes the neck to give good tension. Also, be aware that rifle seater dies that have a crimp function are usually roll crimp. This being the case, you should never attempt to crimp unless the bullet has a cannelure, and then obviously the bullet must be seated such that the neck is crimped into said cannelure. Attempting to crimp a non-cannelured bullet will likely cause the neck to be bulged or crushed. If that happened, the best case is that the rounds won't chamber and the brass will be ruined, requiring you to pull the bullets and start over with new brass. Worst case is that the case could chamber but because the bulge causes less space for the neck to expand on firing, you could see dangerous pressure spikes... which are obviously not good.
The exception is the Lee Factory Crimp Die. It uses a collet to create a pinch like crimp in the neck. This is acceptable for both cannelured and non-cannelured bullets. Some folks swear by this die, saying it greatly improves accuracy and velocity consistency, but I'm not thoroughly convinced of its benefit.
Mike