I've taken this combo at least 100 times without issues, you can take both... The word safe would be a bit of overstatement though when tramadol is involved in anything. I'm sure kratom will only further lower the seizure threshold but so long as you keep the doses minimal there's not much to worry about as far as serious interactions go, especially things like serotonin syndrome. It would probably be best if you stick to one though, they're both cross-tolerant.
Just to comment on the above post, it's pharmacologicaly impossible for this combo to induce serotonin syndrome. Also, most grand mal seizures come without warning. It's much more likely that the clash of kratom's adrenaline release and tramadol's serotonin activity induced some tremors and anxiety (which are not to uncommon side-effects of both) issues that manifested itself as a much worse serious interaction, as opposed to approaching "serotonin syndrome". (which is way overused on the internet these days)
SS is actually far, far more rare than people make it out to be. The vast majority who say they have had it really didn't. I've lost count how many posts I've seen on the boards about either having or coming close to developing SS but almost always the presentation is atypical. It's a very painful and unpleasant experience and you would know if you've had it. It would guarantee a trip to the hospital.