Sentinel+ recorded the costume parts from a character's costume slots; however, it recorded them in a non-CoH naming convention:
<part>Tight !Hips_V_Stealth_01 !Hips_V_Stealth_01_Mask 00003855 00003d00</part>
The 'Stealth' legs part, in the 'Stealth' pattern with, IIRC, colors of green and gold.
Some of them are more obscure, such as a custom weapon:
<part>none none none 00ffffff 00008cd4 00002a7f 00003d00 WEAPONS/Custom_DualBlades/Fem_DualBladeLeft_Falcata01.fx</part>
So it's a non-trivial task to read the costume section of a Sentinel+ save file and reconstruct the costume from it, although I have no doubt that it would be possible to write a tool that would read a file and write a .costume file that could be imported into Icon.