A client's site populates registered user's profile pages by way of dynamic content.
Would this be indexed differently / crawled differently by Google as opposed to a static HTML page?
My thoughts are that it would not be crawled in full as potentially the info could change and be refreshed constantly?
I'm assuming this is not a simple question about 1 site dynamically creating pages from the sites's own database. At least I hope not! That answer is fairly simple, you've only got to look at google indexing this forum, e.g. forum threads updating regularly, for that answer. The answer is if the site is architected in a similar way to this forum, php sending out html on a fairly static (unchanging) url, then that's usually fine.
Here is one other possible interpretation I'm reading from this question...
User profile pages that pull in data from external websites, e.g. a profile page that pulls in and displays the user's latest tweets from twitter, their recent facebook updates, their recent blog entries, etc.
The answer to this particular question depends upon how the external data is pulled in. If it is pulled in server-side in say PHP, then output as html, then it should be indexed. If it is pulled in browser-side from Javascript in the HTML page, then there is less likelihood that data would be indexed.
And finally, if the profile pages are private, like they are in this forum, so that only logged in members can see them, then it is more likely that google wont be indexing them anyway.