So, I noticed that Tier Halibel when using her Ola Azul, unleashed a wave of intense pressurized spirit energy from her sword. This reminded me of Ichigo and Isshin Kurosaki's Getsuga Tenshou attack. So my question is, are they similar, or is there some huge difference between them?
Ola Azul can enhance the user's sword strikes, while the regular Getsuga Tensho cannot.
The Ola Azul is a technique exclusive to Harribel, since it is created by pooling reiatsu within her blade's empty space. This concentrated reiatsu can either be shot as a short-blade shaped projectile, or kept within the blade to increase Harribel's striking strength. When used in melee combat, Ola Azul has been shown as a ribbon of light increasing the width and range of Harribel's attacks :
On the other hand, the Getsuga Tensho is a concentration of reiatsu which is released by the tip of the user's blade. It cannot be kept around the blade to increase the user's striking strength ; the sole exception are Tensa Zangetsu's Getsuga Tensho. In essence, the power of Tensa Zangetsu is to "compress" Ichigo's reiatsu around himself, drastically increasing his strength and speed (as commented in Chapter 163, pages 19-20). This aspect partly manifests as the black robes donned by Ichigo. Tensa Zangetsu can "capture" a Getsuga Tensho when released and wrap it around Ichigo's blade to increase striking strength.
In effect, they are not hugely different techniques ; but the creation method is quite different and sets them apart.