He's not a professional.
He's an amateur using various brands which are mis-matched.

One critical guideline for drip & sprinkler systems:
All parts must be from the same manufacturer.

It is possible, and not uncommon to cut and glue to sched 80 nipples. they are frequently used as above ground alternatives to regular white PVC pipe as they offer greater durability and UV resistance to above ground parts such as the point of connection and risers for spray nozzles. many 'gray risers' I would not recommend attempting to cut and glue to. Sched 80 is a smooth solid pipe with milled threads at either end. it is marked with ink along it identifying it as sched 80 and PSI rating and so on. this is quite allright to cut and glue. Sched 80 should also fit all the same PVC slip fitting snugly (very snugly in most cases!)

if you have a fitting that has been glued on 'un-snugly' don't count on it to last. they may well last a while, but failure is more likely than in a properly glued fitting.... especially above ground where extra forces are at play.

I would need to know what sort of riser it is before I could answer the second question. it is possible there is a solution that doesn't involve digging 2 feet :)