A lot of diabetics are prescribed aspirin. This is something to consider if having a tattoo as this will effect how easily you will bleed and will take longer for the bleeding to stop.
If you have good control with your sugars there should be no problem.
I have a tattoo on my foot & had no problem at all with it healing at all, as long as you follow the cleaning instructions given by tattoo artist & make sure it is a properly qualified tattoo artist & the studio is clean, etc.
I have actually had the tattoo covered with another, also with no problems.