I understand that I can create a product using the shopify product API
but am I at all able to bulk import a group of productswith custom html product descriptions in the form of a .csv like I normally would on the shopify products tab?
There's no direct way via the API to upload a CSV file of products, but you could replicate this functionality in your app. You could set your app up to read and parse CSV so the fields in the CSV map to the fields to Shopify's product model. Then you can use the Shopify Product API to create new products or update existing ones in the user's Shopify store.