I personally know an [name_m]Angus[/name_m]. I never thought anything negative of it. I always thought it was fairly rugged sounding.
It is a name that is going to garner some unwanted attention like angoose and anus. But kids will find something to poke fun at regardless.
Overall I think it’s a great strong name and from the sounds of it, it holds great personal meaning as well. I think as long as he has a middle that he can go by if he so chooses when he’s older, that might be a good compromise.
[name_m]Angus[/name_m] isn’t my style, but there isn’t anything wrong with it, in my opinion.
[name_u]Gus[/name_u] is great. 
I have to agree with [name_m]Angus[/name_m] reminds me of the beef too much and if you just remove 1 letter you have anus. I’m trying to put myself in a child’s position and wonder if people with that maturity (or lack of) would tease him and, sorry to say, I think it’s a name that could make him a potential easy target. Kids do tease kids for anything these days, but making him an easy target won’t help.
The name itself? Nothing wrong with it. The anus and [name_m]Angus[/name_m] beef ties to the name? Gives it something wrong with it.
Also, I [name_u]LOVE[/name_u] the name [name_u]August[/name_u] and [name_m]Augie[/name_m] is not on my nn options, [name_u]Gus[/name_u] is. [name_u]Gus[/name_u] is adorable and I think [name_u]August[/name_u] nn [name_u]Gus[/name_u] is sweet.
I had a student named [name_m]Angus[/name_m] that actually inspired me to use a similar name for our son. His name was never a factor for him. Kids can find anything to be mean about. As above poster said [name_u]August[/name_u] is a good option too.