The pellets by themselves will not make good substrate. Remember, the oak pellets are not decayed wood, they are essentially pulverized oak wood straight from the log, they use soybean oil to keep it well lubricated (a very minimal amount), but nothing else.
I use oak pellets as filler, and filler only.
Over time, since I do recycle my substrate (what is usable anyway) it does decay to some extent. You can also decay it yourself, but you are looking at 6-8 months of decay for it to be somewhat usable.
A substrate I make with pellets includes real decayed wood, oak leaf mulch, manure, and less than 30% pellets.