[Bob Steele]

Short answer...
As long as the outside corners of your robot have at least 8" of bumper on either side of the corner...this is certainly legal.
i am not sure what you mean by Slanted Bumper ends..
You may NOT, in my opinion, use the bumpers functionally by changing their specifications (ie make them slanted in at the dotted portion)

Bumper specifications are given and they must be finished in the way they are described. If Bumpers play another direct role... or have some other functionality, they are not bumpers but part of the robot and would have to be contained within the frame perimeter.

Of course if you can think of a way to use a bumper (as specified and constructed in the rules) they can have a function.

i hope this makes sense... I will give an example... if you had bumpers that slanted in (or out depending on your frame of reference) last year to help the balls enter a collection system that would have been illegal. You could have an opening in them but you may not change their construction..

You could have part of your robot that slanted in... and it could look like a bumper... but it would be counted as part of the robot and have to be inside the frame of the robot at the beginning of play.