No

All weapons have weapon category (pg.279) such as simple, martial, or advanced. Weapons also have other traits, such as agile. The Rogue sneak attack feature (pg.181) requires the use of either:

• A melee weapon with the agile or finesse trait
• An unarmed attack with agile or finesse trait
• A ranged weapon

As you said, the Ruffian racket also allows you to sneak attack with any simple weapon.

A weapon you utilize through the Unconventional Weaponry feat can only be used with sneak attack if it fits into one of those categories. Unconventional doesn't change the weapon category, it only changes how you calculate your proficiency.

So no - it's not true that any weapon accessed through unconventional weaponry qualifies for sneak attack, because it's not automatically a simple weapon. However, if you choose an uncommon simple weapon (such as a clan dagger or katar) you can use it for sneak attacking.

Via Boons

@willuwontu's answer is correct and guaranteed, just not available to all classes; it is also theoretically possible to get access to Spiked Chains via boons. Spiked Chains are marked as being a standard PFS option (meaning normal rules apply to it), and the rules for PFS options state:

Specific boons—such as from the Achievement Points system or Chronicle Sheets—can also grant access to these options.

One such boon is "Avid Collector - Core Rulebook", which contains the Spiked Chain (see this blog post on Paizo.com). It costs 20 AcP. Credit to @Ifusaso and @YogoZuno for finding this!