In Paradise, Nevada, The Clark County Commission is the governmental organization that governs and runs Clark County, providing services.
Paradise is an unincorporated area.
I heard that the services are energy supply, sewer, street security, etc.
Is it true?
Judicial and law enforcement services are provided by Clark County. A private party can't operate those services. Paradise is also served by public school districts.
A county government could provide the other services, but I have not been able to ascertain if it actually does so authoritatively. One source (which isn't particularly authoritative but does provide a clear answer) states that these services are provided by the Clark County government n Paradise, NV. But this source (which also isn't particularly authoritative) strongly implies that these services are (or at least were in earlier days) provided on an ad hoc basis by contributing casinos working together with each other, although the same source later also implies that now, most governmental services in Paradise are provided by the Clark County government.
The time distinction is material.
Prior to the invention of practical air conditioning and the construction of the Hoover Dam to provide affordable electricity to power it, Clark County was basically unlivable, and Las Vegas was an unexceptional small town in the middle of nowhere. The county's tourism based economy's growth also relied upon the invention of commercial air travel and the building out of the interstate highway system which were 1960s and 1950s developments respectively.
So, until much later than most modern large cities, the services needed were far fewer and informal cooperation was more viable. Even in the mid-1960s, Clark County was a tiny shadow of what it is today that was just beginning to show a glimpse of what it would become.
This is illustrated by the population of the neighboring municipality of Las Vegas (per the Census Bureau):
Unincorporated urban Clark County had in addition 561,693 residents in 2000 and 832,310 residents in 2009.
An HOA or special district government could also provide the other services, but I found no sources suggesting that this is what happens in this case, and the timing of development of "the Strip" isn't a good fit to the time frame in which these non-municipal alternatives to municipal government were widely used.