Riyadh buyers are not diversifying out of a currency, since the riyal and the dirham are both pegged to the dollar. They are buying access: a two-hour flight, a summer residence out of the Riyadh heat, and a market with deeper branded residence and beachfront supply than anything available at home. Use comes first in almost every Riyadh conversation, and yield is what makes holding it through the rest of the year sensible.
Rules that apply to every buyer in Saudi Arabia are covered in the full Saudi Arabia buyer guide. This page covers what is different in Riyadh.
Yes. You can let it on a standard annual tenancy, or operate it as a holiday home under a Department of Economy and Tourism permit, which is what most owners who want the unit available for their own use choose. A management company handles licensing, guests and cleaning for a share of the revenue.
No meaningful risk. Both the Saudi riyal and the UAE dirham are pegged to the US dollar, so the rate between them is effectively fixed. Your cost is the bank's transfer fee and spread, not exchange rate movement.