Qucik Tau Questions

[Demonus]

Playing a 2v2 game with IG + Tau and the following situations came up:

IG using Tau marker lights to remove cover and increase ballistic skill. Is this allowable, or are these abilities useable by Tau only?

Assisted Overwatch, wherein IG tanks were charged and 4 nearby Tau units fired overwatch. Again is this allowable, or does it only work if a Tau unit is charged?

Seems a little overpowered when other Codices state "units from codex X only"...

[RGilbert26]

Unsure about other armies using markerlights but the Tau overwatch special rules specifically states that only units with the rule can help other units being assaulted if they are within 6". Not sure why you guys missed that one, just read their codex.

[Magpie]

First line, second paragraph of the "Target Aquired" special rule

"Immediately before a unit from Codex: Tau Empire shoots at
a target that has one or more markerlight counters, it can
declare it is using one or more of the markerlight abilities
listed below."

[Sparky]

Supporting fire can only be used to support 'friendly unit'. This is tau, generic space marines and eldar due to being battle brothers and all.
So no love for the guard.

And Magpie has the marker lights summed up.

[Demonus]

Excellent thanks for the clarifications. :)
As for missing it, it wasnt my codex, Ive never played Tau (or against them before) and apparently the guy who did can't read =P