I would say yes, the angle on the tensioner is too great. You should level that out as much as you can while still maintaining chain clearance of the frame stays. You may have to take out a link or two, which can be a daunting task if you haven't any experience at it- and you need a decent chain cutting tool.
Are you having some kind of problem? You still have a lot of dropout left if you want to pull the wheel back- that will level out the chain a bit, but the idea is to chain the angle with the chain tensioner the least you can get away with. You may have to adjust the brake pads then.
I don't know about the beveling suggestion- Is that for a smaller 410 chain? I don't know what chain you have- most common is 415 and the sprock shouldn't need any special grinding. The sprocket is often countersunk on one side- make sure you're getting the benefit of allignment and frame clearance with the countersunk on the most appropriate side for your build. It appears you have the countersunk facing so you get the moist frame clearance, which is good- IF you are getting good allignment of the motor and wheel sprockets.
Here's a tip for the long run- a smaller sprocket helps give you not only a faster top end, and less noise and less revving in the midrange, it also helps frame clearance issues by making a smaller arc for the chain- Unless you are very heavy or riding a lot of mountains or off road.
I never use a chain tensioner on my cruiser fframes with 34, 36 and 39 sprockets- your Mountain bike frame may have less clearnce and a smaller sprocket might relieve any clearance issues. Your motor is pretty high on the frame and appears it may be sitting at a bit of an angle- but the back mounting looks square to the frame- if you could get the motor sprocket lower I think it would help, but then you may have other chain clearance issues.
If you are going to ride primarily on the road, you may want to get some smoother tires- those knobbys will give you a lot of vibration at speed. I 'd recommend 26 x 1.5 or 1.75 to give a great roll and weigh less.