It isn’t uncommon for sellers to work on multiple orders as they need to. It really depends on the individual style of the seller. I don’t think it’s a big deal to message a seller once in the of a project if you are polite and have a genuine question, but otherwise it’s really good to let them just do the job in their own time. A lot of sellers take a request for updates to mean that you’ll let them know if you think of something you really need to tell them or ask them. If you actually want them to just message you so you know they remember your order, just ask them if they are willing to commit to daily or every other day messages before you order.
Since many Fiverr sellers offer or do custom micro-jobs (5-15 minute tasks for $5-10) even one message back and forth can cost them part of their earnings for the day. This is even more true with sellers that have a lot of experience. They can work that into the price of the offer if it is your requirement. @eoinfinnegan is exactly right that on a longer job, messages can break the deal.
New sellers are often quite a bit different on this although it still depends on the type of job and the seller work style. They need work and they need reviews, so a level 0-1 seller may accommodate you with these kind of requests for free. It’s part of how they earn their way up in some cases, but it’s still best to ask in advance and be sure they understand your expectations so they can decide if the job is a good match for them.