They will fire HE at armoured units if given a fire order, also bombard if capable (from memory the 65mm isn't (in game)).
The Greek formations are fairly paltry - there are no formal AT weapons in the XII Division
at all, and only 8x 45mm ATG, 4x20mm ATR, 4x 20mm Flak and 4x 37mm Flak (captured) in the 19th Motorised Division.
In this world, a PzI or PzII is a formidable tank... how different barely a month later in the Soviet Union

Of course, even without formal AT weapons, tanks are vulnerable to all manner of misfortunes.
I would like to see the demise of the 4 attack types for the gun, and a handling of ammunition types instead, with the four roles allocated to the ammunition.
This would allow HE ammunition to have an emergency AArm (although except for larger guns this is modest - only a threat to light tanks and half-tracks), or for mixed loads of PzGr(rot) and SprGrHl, or APC and APDS for 6pdr and 17pdr guns, and AP and HVAP for US guns - it would also allow dual use of Heat ammunition as emergency APers ammunition... this is vital to account for modern weapon practices, where M1A1 in ODS for example had mixed loads of M829, M829A1 and M830 (HEAT) for anti-armour use, and used M830 as the only OR round from the tank gun.
It would also be good to move the V0 information from the gun to the ammunition "as fired from gun xx", as the muzzle velocity of HE, AP and HVAP can show considerable variations from the same ordnance.