Irish is not a pro-drop language, no. You need the pronoun to indicate who is doing the action. Dropping the pronoun (note: this doesn't happen in the mé and muid (and other forms, in Munster Irish) - you merely are using a synthetic form that still encodes the pronoun) is not allowed in Irish.
Saying ólann would be the equivalent of saying "drinks"
Tá sé ag ól means "He is drinking".
In Irish and in English, the simple present (Olann sé/He drinks") and the present progressive (or present continuous) (Tá sé ag ól*/"He s drinking") are not equivlent - they have distinct meanings, and you can't translate from the simple present in English to the present progressive in Irish, or vice versa.