App owners do bet on their own sites, however they make up a very minor portion of the site volume.
Let me help in crunching down some simple number to help understand this.
Assuming that an app owner wager 100 bitcoin of volume in his 1 % house edge site, that gives him half of the house edge back to him as app owner
So 50 % of 1 % house edge * 100 bitcoins = 0.5 bitcoin
Assuming that there is no variance or anything at all, he will lose 1 bitcoin for every 100 bitcoins volume
Which means he lose approx 0.5 bitcoin every 100 bitcoin volume
In the end it will be the same as normal player betting on a 0.5 % house edge?
P.S : Is the share of app profit still 50 % of the house edge?
Your calculation is right. So basically, it is like losing 1 btc but you still are able to get back 50% of it which is 0.5btc back. However, i remember that it is not 50%. I remember there is one time i hear that it also factor in on the fee for campaign signatures and some other misc stuffs.