The Noveltech Character and Vocal Enhancer use similarly advanced techniques for optimizing audio in a simple and intuitive way. So in a sense, one could use the Vocal Enhancer for instruments and the Character on vocals. However, the algorithms in each plugin are entirely different, which is why they were each designed specifically for their own general purpose. They were each optimized for their own task.
Notice that on the interface of Vocal Enhancer, there is a frequency graph that spans the critical range normally associated with vocals; there is also a parameter for low/high frequency focus to add either body or presence. These parameters are designed to be lucid enough to convey the effect of the parameters you adjust. On the Character, controls of this type are more nebulous, allowing for a more intuitive approach to a wide array of timbre and tonal types; you have three modes and a range of 'Target' to dial-in a setting that works for your content. Of course, both plugins may have some overlap in terms of effects that can be accomplished, but they each have their own way of going about it, and their own interface for doing so.
It's like comparing two EQ plugins, let's say the Mäag EQ4 and EQ2: could you treat frequencies with both? Yes. Are they both great for adding Air and transparency to instruments and vocals? Absolutely. But I always use the EQ4 on vocals because it has both boost and attenuation for each band, which focuses specifically on vocal frequencies. I always use the EQ2 for instruments, because I can adjust the bandwidth for a variety of different frequencies and extract focused character and body with minimal tweaking.