Sorry, but thats simply not true.
1. Charge the Berserker only if they have a line of sight.
Your own skirmish line blocks line of sight for shooting, not charges or berserk movement. you'd need to make it a formed unit to prevent Berserk discharge.
2. Have your own skirmishers deployed in front of the hirdmen a free 4" move.
So you're going to slow down your entire formed hirdmen unit, in the vain hope that your skirmishers can see off my skirmishers? If you're deploying Hird skirmishers, that's fine by me, points not guarding your flanks (where the skirmishing pirates or hird are best deployed). Also the fact you're slowing down your assault works for me too, gives me more time to outflank you (the best tactic versus the numerically inferior Vikings).
3. Is no need for the hirdmen to run to close behind the skirmishers.
Works fine by me, see above! Your 'need' to not have your berserks wasted slows your entire army down, surrendering the initiative to me.
I don't mean to be rude Goltron; I've played numerous games versus my Viking counterpart, he dropped Berserks early on as I was far too good at dealing with them.
As for them being too good, yes they can be. I won't use 'em, not unless my opponent is being nasty (like Normans with lances).