Can iPads and iPhones pick up satellite signal for using GPS location?

Only WiFi+Cellular models of iPad have integrated GNSS/GPS capabilities - this being a function of the iPad Cellular chipset.  All models of iPhone also have built-in GPS - and benefit from aGPS (Assisted GPS) to derive location using both GPS and Cell-ID data.

WiFi Only models of iPad have no GPS capabilities with which iPad Location Services can derive location. This fundamental difference may significantly impact your ability to use mapping or other Apps that require precise location data - in particular if real-time positioning (e.g., a moving map) is required.

WiFi Only iPad models can only “infer” their location from a database lookup of neighbouring WiFi networks for which the geographic location is known, or the geographic location of your public IP address. For static applications in urban locations, where the location of IP public IP addresses and WiFi networks are known, an “inferred” location can be relatively accurate. However, in rural locations, or when using a Cellular/Satellite/VPN connection, location accuracy of an inferred location [if it works at all] may be very inaccurate. 

Choosing a cellular model does not commit you to adding a cellular service plan for the iPad, but ensures that you have immediate access to GPS/GNSS and precision positioning services.

You can use a third-party Bluetooth GPS receiver with both WiFi Only and WiFi+Cellular iPads to either add or augment existing GNSS capabilities.  BadElf and Garmin GLO are two examples.