Yes, your Ruger Ultralight can easily handle any factory round, including the Hornady Light Magnums. As a side note, I personally have never been overly impressed with the accuracy, nor velocity of the Light Mags in any rifle I've fired them in.
Winchester used to produce a 257 Roberts +P load that was excellent. Check and see if they're still available and give them a try before trying the Hornady Light Mags.
BTW, I like Hornady bullets and ammo, I'm just not impressed at all with the overly hyped "Light Mags". Their standard ammo is in my opinion, better stuff. Most of time their claims of "higher velocity" don't live up to advertised velocities.