Don't they have to play a number of games before their salary counts on the cap?

If I recall, in Tomkins' first season, people were speculated we stopped playing him as we didn't want his salary to count... (10 games, maybe?)

1 game IIRC Hull FC fell foul of this when Andy Last came out of retirement for 1 game due to an injury crisis.
His entire salary thus went on their cap and took them over.

It depends if they're counted in the 1st tier or 2nd tier. Effectively the 1st tier is the top 25 salaried players at the club. The 2nd tier is the rest.
Players in the 1st tier are counted on the cap regardless of whether they play a game or not.
Players in the 2nd tier must play a game before they're counted.

The 1st tier cap is £1.65m (plus various clauses/exemptions)
The 2nd tier cap is £75k

O'Donnell will count on the cap, but only the wage he collected. Not his full pa salary.

A comment attributed to the RFL rlat the end of this report

Quote: compromise agreement "The RFL spokesman confirmed there are no salary-cap implications because the regulations allow for such compromise agreements.'"

What "compromise agreement" would that be, then?