This is assuming that Ivankov him/herself doesnt have haki, which im sure he does. Pre-time skip seems to not show anyone using Armandment. Like when Garp punch pheonix Marco (should have showed haki), Rayliegh blocking Kizaru's kick (should have used haki), Shanks blocking Akainu's punch (should have shown haki). Its seems that characters are showing their haki abilities now during post timeskip. Im pretty sure if Sabo has Armandment Haki, then Ivankov also does since invankov was the right hand man of Dragon for years.@bold If anything he was "struggling" more with Smoker than Sanji. With Sanji, he didn't have to resort to using haki against him. Not to mention, Sanji's fight lasted a few pages and Smoker's fight was a lot longer. Ivankov stops at Vergo, I can't see him hurting Vergo through his FBH.
And if Ivankov does have Haki (which he definatly does) then he easily crushes vergo, as his hormones would make him stronger, faster, and more impervious the physical damage.