Sometomes you can't mix an oil with stuff.
For instance,NEVER use an oil and sulfur compound together.
Moisture and sunlight cause a reaction that is nasty for your plants - burns the leaves up.
I don't know for sure if Magnesium Sulfate reacts with Oil.
Sulfur and Neem are both organic - it doesn't mean squat.
The reaction is what happens when most oils and sulfur mix.
Also Lime Sulfur is different than Fungicidal Sulfur.
Most Sulfur Products have a warning about using Sulfur products with oil.
I see warnings from waiting a week to 4 weeks after spraying various Sulfur products.
As I said,I don't know if Manesium Sulfate is strong enough to worry about.
I do KNOW that mixing Safer Brand Garden Fumgucide and Neem sucks.
Gotta wash off the oil first...
I sprayed Neem one day to get rid of spider mites.
Sprayed the Fungicide (12% sulfur) the next day at sunset (Sulur is a no no in the sun - creates sufuric Acid with water+sun).
By morning my plants dropped almost all their leaves.
Screwed them up big time within hours after the sulfur spray.
I used the fungicide as a preventative measure to get rid of broad mites that were also present.
Neen didn't work on them.
A hint for Spider mite control.
As it cools off at sunset they gather in clumps in the webs.
Spraying them seems to be more effective when they gather together.
Also I only spray my plants with anything after they are out of direct sun light...
I'd use caution with oils and Sulfur / Sulfates.
I'd guess you would already see if you screwed up,when I did the bad news was delivered very fast to my plants...