The organization that certifies guides in the United States is called the American Mountain Guides Association (AMGA). Guides can be certified as either Rock, Alpine, or Ski guides. Each form of guiding is called a discipline and each discipline involves 3-4 courses and exams leading to certification. Each course and exam costs between $1600 and $2000 and lasts between 6 and 11 days. It usually takes a working guide about 3 or 4 years to become certified in a discipline. As guides can be working toward certification in multiple disciplines simultaneously it is possible to get through all 3 certifications in about 5 years.
In the United States guides are not required to be certified. Most insurance companies and land managers have very basic requirements for guides which include things like: basic first-aid training, CPR cards, and a climbing resume detailing experience in the terrain where they are guiding.
Certification ensures that an objective, outside party has examined your guide on the most challenging guiding terrain over a substantial period of time and determined that they are physically and mentally able to handle the task. Certified guides have met very high standards in areas such as route finding, navigation, climbing and ski ability, camp craft, improvised rescue, etc. The AMGA Alpine exam lasts 10 days, the AMGA Ski Exam lasts 8 days, and the AMGA Rock exam lasts 6 days. You are certainly not under any obligation to hire a certified guide, but you need to realize that only certified guides have been examined before guiding. There are many very competent guides who are not certified.
These days we don't do a ton of guiding in places where we have never worked previously, but we do sometime visit new ranges or new mountains within a given range. When we were examined as guides the goal was to examine us on terrain we had never seen, as "onsight" guiding is considered the standard for a fully qualified guide. When a guide goes into a new area they do a lot of homework by speaking with other climbers and guides, reading guidebooks, visiting websites, checking weather reports, and looking at maps. Although different routes present different challenges, after awhile a pattern emerges and guides use similar techniques on different mountains to solve similar problems. One benefit to going to a new area with your guide is that you can be certain the guide has put a ton of thought into that trip and usually the thrill of new terrain becomes infectious.
The short answer is no. Unlike some countries the United States requires different permits for each State Park, National Park, US Forest Service District, Bureau of Land Management district, etc. Perhaps the original idea was for each land manager to have the option to manage their particular area in a way that maximized both use and protection of the resource. While this plan has done an excellent job of protecting our resources (perhaps still the most important thing) it has made it difficult for guides and even big guide services to work in a wide variety of areas. This system has created guides that are very good at climbing individual mountains, but may not be permitted to climb a similar peak on the opposite side of the same valley. We have extensive connection at other guide services and an unusually large number of permits for a small guide service, but there are still a lot of places we cannot take you. Land managers seem to be slowly realizing the need to provide at least limited access for credentialed guides (such as
AMGA and IFMGA) but the government works slowly and some areas may not open for years.