There is nothing wrong with IS troops using ClanTech, if they can manage it. During the FCCW, some of the elite DCMS units have a very high amount of ClanTech in their ranks (1st Genyosha: 45% ClanTech, Otomo: 45%, 1st SoL: 33%, 2nd Dieron Regulars: 50%, etc.).
Rasalhague, Lyrans, FedSuns, and ComStar also use ClanTech regularly, as do a few merc units. The only ones with little to no ClanTech are the Capellan, the FWL, Periphery natiions, and WoB.
Some ClanMechs are even common enough in IS ranks to be listed in RATs. The DCMS RAT of 3067 e.g. includes Stormcrow, Ebon Jag, Direwolf, and Mist Lynx; that of the AFFS includes the Mad Cat Mk.II; 2nd SLDF has Nova Cat and Supernova (not only for the Nova Cats but also for IS units like 1st Royal BattleMech Regiment); etc.
So, no need to feel dirty.