I have the Tamron 28-75 and have only recently started trying IR photography using my Hoya R72 filter with it.
The images I've gotten so far have had a hotspot; the hotspot is less noticeable than some other lenses I've used, but it is still there.
I have only used the lens a little bit with my IR filter and must say that although the hotspot is commonly caused by the lens coatings, I feel that there are techniques that may or may not help in reducing or eliminating hotspots regardless of the lens used.
I'm sorry, I don't have any sample images right now. I will try to post some as I get some processed, but as I'm an automation programmer, I'm quite lazy!