There's nothing wrong with it. I don't think that there's any rule against it in any other leagues either but could be wrong. If one thinks about it, if you can't make a trade and you don't have a farm team, how else do you bring in a body if you need one?
I'm not sure if Duke Williams was signed after the deadline or not, I do not recall, but Begelton definitely was. Nothing wrong with that. If the Bombers want to bring in Streveler now, let them. I suppose that he's an upgrade on who they have now but if he plays for them you can cut one-third of their offense right out of the playbook. I'm actually shocked that Arizona would even give a guy with no deep ball a chance at all let alone for that long.
I like Streveler, he's fun to watch, but he has no future leading any team with his skill set. He had a good run, a good sample size in 2019, and it proved that Winnipeg was an excellent team with a QB that could make all the throws (Nichols or Collaros) and were one-dimensional and average at best without one (Streveler).