I don't think the rule about the omission of 'o' before a vowel is always applied, especially in scientific names, see the list below. It mainly applies to more common and older terms such as monastery for instance.

Mono-:

• One; alone; single: monocoque
• Chemistry (Forming names of compounds) containing one atom or group of a specified kind: monoamine

(ODO)

Mono:

• word-forming element meaning "one, alone; containing one (atom, etc.)," from Greek mono-, comb. form of monos "single, alone," from PIE root *men- "small, isolated" (cognates: Greek manos "rare, sparse," Armenian manr "thin, slender, small," and perhaps English minnow).

( Etymonline)

List of English words prefixed with mono- in alphabetical order.

As for mono objective you can find both forms, and in the end it comes down to a matter of style and preferences:

• A mono-objective evolutionary algorithm for Protein Structure Prediction in structural and energetic contexts

• ... 1 time 25 0.1 hand lens, 10 times 32 0.1 stereoscopic, compound microscope, 100 times 16 0.25 monobjective, compound microscope, 250 times 8 0.50 monobjective, compound microscope, 500 times 4 0.95 limit, air-immersion objective, ...

I don't think the rule about the omission of 'o' before a vowel is always applied, especially in scientific names, see the list below. It mainly applies to more common and older terms such as monastery for instance.

Mono-:

• One; alone; single: monocoque
• Chemistry (Forming names of compounds) containing one atom or group of a specified kind: monoamine

(ODO)

Mono:

• word-forming element meaning "one, alone; containing one (atom, etc.)," from Greek mono-, comb. form of monos "single, alone," from PIE root *men- "small, isolated" (cognates: Greek manos "rare, sparse," Armenian manr "thin, slender, small," and perhaps English minnow).

( Etymonline)

List of English words prefixed with mono- in alphabetical order.

As for mono objective you can find both forms, and in the end it comes down to a matter of style and preferences:

• A mono-objective evolutionary algorithm for Protein Structure Prediction in structural and energetic contexts

• ... 1 time 25 0.1 hand lens, 10 times 32 0.1 stereoscopic, compound microscope, 100 times 16 0.25 monobjective, compound microscope, 250 times 8 0.50 monobjective, compound microscope, 500 times 4 0.95 limit, air-immersion objective, ...

I don't think the rule about the omission of 'o' before a vowel is always applied, especially in scientific names, see the list below. It mainly applies to more common and older terms such as monastery for instance.

Mono-:

• One; alone; single: monocoque
• Chemistry (Forming names of compounds) containing one atom or group of a specified kind: monoamine

(ODO)

Mono:

• word-forming element meaning "one, alone; containing one (atom, etc.)," from Greek mono-, comb. form of monos "single, alone," from PIE root *men- "small, isolated" (cognates: Greek manos "rare, sparse," Armenian manr "thin, slender, small," and perhaps English minnow).

( Etymonline)

List of English words prefixed with mono- in alphabetical order.

As for mono objective you can find both forms, and in the end it comes down to a matter of style and preferences:

• A mono-objective evolutionary algorithm for Protein Structure Prediction in structural and energetic contexts

 
• ... 1 time 25 0.1 hand lens, 10 times 32 0.1 stereoscopic, compound microscope, 100 times 16 0.25 monobjective, compound microscope, 250 times 8 0.50 monobjective, compound microscope, 500 times 4 0.95 limit, air-immersion objective, ...

I don't think the rule about the omission of 'o' before a vowel is always applied, especially in scientific names, see the list below. It mainly applies to more common and older terms such as monastery for instance.

Mono-:

• One; alone; single: monocoque
• Chemistry (Forming names of compounds) containing one atom or group of a specified kind: monoamine

(ODO)

Mono:

• word-forming element meaning "one, alone; containing one (atom, etc.)," from Greek mono-, comb. form of monos "single, alone," from PIE root *men- "small, isolated" (cognates: Greek manos "rare, sparse," Armenian manr "thin, slender, small," and perhaps English minnow).

( Etymonline)

List of English words prefixed with mono- in alphabetical order.

As for mono objective you can find both forms, and in the end it comes down to a matter of style and preferences:

• A mono-objective evolutionary algorithm for Protein Structure Prediction in structural and energetic contexts

• ... 1 time 25 0.1 hand lens, 10 times 32 0.1 stereoscopic, compound microscope, 100 times 16 0.25 monobjective, compound microscope, 250 times 8 0.50 monobjective, compound microscope, 500 times 4 0.95 limit, air-immersion objective, ...