It could be argued that, as the Uruk-hai swords have a pretty nasty-looking spike on their back sides, they could be used to pierce armor like picks, and hence would be elligible for using piercing strikes. What is your opinion on this matter?

As you say, they are Uruk-hai swords. And being swords, they have the special strike related to swords. The rulebook specifically calls the berserker's weapon a sword, and as it happens, Adam Troke himself answered this question online some time ago with a simple 'No.'.

Got it, thanks!