Dropshipping is a challenging area, and I don't mind telling you that 80% of sites that start up in this area do not last longer than 6 months.
Remember... you are (or will be) one of MANY sites selling identical products as dropshippers like to have as many people as possible setting up websites to sell their goods. The more people selling for a dropshipper, the more competitive it becomes, and the PRICE is the key factor in getting business.
Then, it becomes "a race to the bottom" as competing websites try to attract business for the same products, by offering the cheapest price.
These days, people shopping on the internet are very clever... they know when a lot of sites are selling for dropshippers, and they know that they will be getting exactly the same item regardless of who they buy it from - so they look for the cheapest price.
Your dropshipper does not care what you sell his good for. He knows that he gets HIS price, because that's fixed for you (and everyone else), so if he has a product which costs you $10 to buy from him to send to someone else, he does not care if you sell it for $10.01 . He knows he will get his $10, and after you have paid him, your profit is what is left over... in this case, one cent.
SO...
It is better to keep away from dropshippers selling cheap stuff (no margin)
It is better to keep away from dropshippers who sell branded goods (electronic goods, cameras, dvd's, CD's, games...) ... all these are a NO-NO...
It is better to keep away from dropshippers who have LOTS of re-sellers. The more competitors, the greater the pressure on price.
Stick to dropshippers in your own country... AVOID trying to set up relationships with companies in foreign countries.
THEN... consider YOUR customers...
If you represent SEVERAL dropshippers on ONE WEBSITE, bear in mind that each one will be sending goods to your customer. So if your customer orders THREE ITEMS from THREE DIFERENT dropshippers, he has to pay for THREE SHIPPING CHARGES and must wait for THREE SEPARATE DELIVERIES.
And what if the customer wants to return TWO of the THREE items??? Who does he return them to? Who pays for the return shipping?
Dropshipping is very challenging... there are MANY more considerations and you need to investigate this very carefully.
Now... to your original question.
Because different dropshippers will have different shipping charges and systems, you will need a PER PRODUCT shipping system. This is possible to do in Zencart, but it is complex.