Nikki,
I agree with Jaffar that personalities can differ between uros. For this reason, I did not put a lot of emphasis on what I had heard in the past about ornates being difficult to pair.
I recently attempted to introduce a 5 1/2" female ornate to a 5 1/4" male ornate. I had been working with malis and geryi for years and was not prepared for the aggression I encountered with this introduction. The female from the getgo decided that she wanted to kill (not harm, not dominate, not maim) the male from the moment her feet hit the ground. I introduced her to the male’s enclosure, as I knew in advance that ornate females could sometimes be crabby- what an understatement! Hoping to diffuse the situation, I put her and the male ornate in with an adult male geryi hoping that she might forget her aggression towards the male ornate if she had the larger geryi to contend with. Nope, she was not intimidated at all by the larger geryi and climbed right over him to get to the male ornate. She is now in an enclosure with the geryi (do not want her to get used to being solo) with a visual of the male ornate. I hope to reintroduce the two after I put enough weight on the male so that he has a considerable size difference on her. I am not holding my breath for success with this pairing. I spoke to Doug Dix on this situation and he just chuckled saying that ornates (especially females) can be temperamental and that he himself has had problems introducing ornates.
Although one can never tell the future, I would think that pairing uormastyx of the opposite sex would give you better odds of less aggression down the road.
If you do decide to put a mali with your ornate, I would suggest having a spare enclosure set up just in case.