the correct way of using such elements is to use the IDT sRGB-Texture. With this operation you are bringing the element into the “scene”, the same way you would use a texture in a 3D application.
The luminance of the elements stay in their range with values between 0-1. Therefore they might look a bit dark due to the different tone mapping that ACES uses, in comparison with the standard Nuke sRGB viewer, but this also depends on your output colorspace. (I assume out_sRGB or out_Rec709, right?)
The limited color gamut of sRGB is placed in the far bigger gamut of ACEScg. Therefore the colors might appear a bit desaturated.
Use a ColorCorrection node to adjust the brightness, contrast and the colors to to make the elements “fit” in your scene/comp.
Please also check the article Understanding the sRGB-Texture IDT that I wrote a while back.
I hope this helps.