Its been my experience that many of the larger haps are not very aggressive. However during breeding it may increase but other tank mates shouldn't be too much concern as long as they are completely different shapes, size, color etc.... Haven't kept Venustus myself so not sure on them specifically. Make sure they can't fit tank mates in their mouth or they will likely be dinner at some point. And since venustus are large tank footprint and stocking numbers are considerations as to options.
I had a pair of very large Phenos in a tank I bought from a member here. I was initially concerned with the ratio being 1:1 and with there size the smaller tank mates, some 2", would be in trouble. The seller assured me there would be no issues and was right. They were the most peaceful fish I've kept to date.
I know numerous people on here have kept and bred them so I am sure you'll get some good advise specifically to venustus soon.