Yup. Since it is an ongoing effect that requires the abjuration's energy to be present in order for the suppression effect to be engaged, you should therefore be able to remove the suppression effect by cancelling out the abjuration (via Dispel Magic or similar spells). Making it a duration spell that is dispellable however allows me, as the creator, to believably make the spell dismissable thereby giving me an advantage for my disadvantage. Also, if Bim's Magic Supressor were cast at minimum caster level (15th), Dispel Magic would only have a 25% chance of dispelling it (1D20+10 vs. DC 26) and Greater Dispelling would have a 50% chance of dispelling it if it was cast with a +15 to their caster level check.