Title. I was hoping to add this question to SAC.

I don't think so. Dispel Magic can only be used to end actual spells. Oil of Slipperiness isn't actually casting a spell; it's just referencing an existing spell as a shorthand for an effect it's applying.

This is a nuanced semantic debate.

Can you use dispel magic to dispel a magical effect like a vampire’s Charm ability or a druid’s Wild Shape?

Dispel magic has a particular purpose: to break other spells. It has no effect on a vampire’s Charm ability or any other magical effect that isn’t a spell. It also does nothing to the properties of a magic item. It can, however, end a spell cast from a magic item or from another source. Spells—they’re what dispel magic is about. For example, if you cast dispel magic on a staff of power, the spell fails to disrupt the staff’s magical properties, but if the staff’s wielder casts hold monster from the staff, dispel magic can end that spell if cast on the target of hold monster.

There are abilities and other spells that can end or suspend magical effects that aren’t spells. For example, the greater restoration spell can end a charm effect of any sort on a target (such as a vampire’s Charm or a dryad’s Fey Charm), and a paladin’s Aura of Devotion can prevent or suspend such an effect.

Three of the most versatile spells for ending certain magical effects are lesser restoration, greater restoration, and remove curse.

Per the 2014 SAC:

Dispel magic has a particular purpose: to break other spells.

However, it later specifies:

[Dispel magic] works on a spell cast from a magic item or from another source.

I’m uncertain whether WotC intended Dispel Magic to end only cast spells (excluding the spell’s effects conferred without casting), as the DMG 2024 states:

Many items, such as Potions, bypass the casting of a spell and confer the spell’s effects with its usual duration.

Oil of Slipperiness exemplifies this—it “gains the effect of the [...] spell” while “bypass the casting”.