As an Eldar player who fields 4 skimmers, I can tell you right away that you cannot disembark then reembark in the same turn. That is most definitely illegal. Ask him to support it in the rules, he won't be able to.
Remember that the 2-dice wargear (holo-fields) can only be used by Falcons and Fire Prisms (well maybe Vypers can, but you really shouldn't). If he claims it with Wave Serpents, thats wrong also. They have their own special rules, but they can't mix and match.
Onto beating Eldar, 8 havocs sp0rting 4tank-hunting autocannons are to be feared. 8 S8 BS4 shots will cause enough glances to a holo-fielded tank to have a damn good chance of killing it. Infiltrating them is useful to get first turn penetrating hits, but they will then likely get blasted away by the entire remaining Eldar army, so having them in your gunline in a spot with good lines of fire is often just as good unless you have a large amount of infiltrators. Bear in mind that the Eldar player will likely manouvre to avoid their shooting, so you can play accordingly, or will try and destroy them with overwhelming firepower or assault. Castling isuseful to avoid this.
In Gamma games, deploying to be able to get first turn shots is useful as you can then pen the skimmers,the only chance you'll get. Infiltrators are very good for this.
In Omega games, castling your shooting can be very useful too.
Hope this helps.
In Omega, you've just got