I would say that if the mentioned customer plans to implement and use some business applications or high quality services on the network using mentioned types of devices, this requirement is actually very reasonable, as different devices behave on same VLAN network differently (probably customer has experience with that difference, which often is not pleasant). They have a lot of reasons to ask for such test, but they have to pay for the work.
Results with laptop are much better usually (better antenna, more TX power, better drivers, better adapters). You can expect RSSI levels on phones 5-7 db less than on laptop, and performance 2-4 times less in many cases, so there is really a big difference.
But waht is even more important -- with iOS devices version of firmware is very important (some of versions have really nasty behavior, bordering with unusable wi-fi), especially for roaming.
For hotel you probably need not so actually survey, but a test with Speedflex for performance demonstration, works for all platforms.
In case if business applications are implemented (for example, wokflow and tracking using iPhones or iPads) you need actually to make survey on all area using devices to be implemented to provide proof that network will work.
Such survey is additional work (and not very easy), and you can't do it automatically using Ekahau Site Survey or similar tool on iOS devices. You can use Speedflex on any platform, may be even can program some script to map this
results using GPS (or at least make screenshots). It is more manual
labor, but can be done.
For Android you can also use Ekahau Mobile survey (commercial), this is fast and easy to document.
Survey is quit a bit of work, but it is required if any business applications must be reliably used.
In many cases, you probably don't need to survey all areas with all devices, usually testing 2-3 typical areas is enough to have fairly clear understanding about device-specific behavior.
Hope it helps.