I want to control a servo (sg90) with an arduino uno. The servo will be under load for most of the time. Now, I know that the correct way would be to get a servo motor driver, but I was wondering if I could wire some pins on arduino in parallel to get more current out safely.
You will not be powering the servo from any number of I/O pins.
A single I/O pin can control a servo, regardless of load
Which indicates that you do not know how a (modelling) servo actually works.
Bit more research needed there, mate! I know it's tricky finding reputable websites and references.
You will be powering your servo from 5v pin, which should be ok until it is not. So don’t try to cut corners and get a driver
You can CONTROL one or more servos with a Uno without any problems with current.
You cannot safely POWER servos from the Uno however many pins you use. The POWER should come direct from a battery or power supply.
Can you show an example of a servo motor driver? Aside from boards that allow you to control 16 servos instead of the 12 supported by an Arduino UNO itself, I don't know of any 'servo driver'.