I gave myself 16 prowlers, and gave the opponent a bunch of rams (so they would just sit there and take the melee beating). I used one prowler to swing, recorded the damage, then deleted one Prowler and did it again. I went from 16 to 8 Prowlers before getting bored :P

The results -
First - the radius of the pack is not huge. It's hard to measure exactly, but it appears to be maybe 50% bigger than a Fortress.

10% more attack (1.5 damage/swing) per prowler nearby.
5% more hits (8.5) per prowler nearby.

So the formulas are -

Attack = (1 + (n-1)*0.1)*15
Hits = (1 + (n-1)*0.05) * 170

where n = number of Prowlers in a pack. It's n-1, because 1 Prowler does not benefit itself (tested and confirmed).

The Damage Dance of the firepit DOES work on the entire attack value -

8 Prowlers
1 Prowler swings at Ram with no Damage dance = 25.5 damage
1 Prowler swings at Ram with Damage dance (30%) = 33.25 damage (it did 33 damage 3 swings and 34 one swing).

33.25/25.5 = 1.30, or 30% more damage.

I have not tested whether the Tashunke effect only works on Base Damage/Hits, or upgraded (if you sent cards or researched techs to upgrade those stats. The Tashunke does not have a normal upgrade at higher ages.)

My conclusion is that the Prowlers must be massed to not be useless. Even then, a full squad of 12 has the following stats-
225 resource 2 Pop unit
31.5 Attack 2 splash area
263.5 Hits
Can Stealth.

Elite Axe Rider
200 resource 2 pop
43.75 Attack
315.5 Hits

They both have 10% ranged resist. So for 2/3 the cost I can have Curaissiers... with half the hit points, get weaker as they die off, but stealth.

Ya.

Stealthed raids might be good... but building fire is an issue for their low hit points.